Systems including an apparatus comprising both a humidification region and a dehumidification region with heat recovery and/or intermediate injection

ABSTRACT

Embodiments described herein generally relate to apparatuses that include a vessel comprising a humidification region (e.g., a bubble column humidification region) and a dehumidification region (e.g., a bubble column dehumidification region), and associated systems and methods. In certain embodiments, the apparatuses are configured to include various internal features, such as vapor distribution regions and/or liquid flow control weirs and/or baffles. In some cases, the apparatuses are used in water purification systems, such as desalination systems. The water purification systems may comprise additional devices external to the apparatuses, such as one or more heat exchangers, one or more heating devices, and/or one or more cooling devices.

TECHNICAL FIELD

Embodiments described herein generally relate to a water treatmentapparatus comprising a humidification region and a dehumidificationregion, which in specific embodiments may be a bubble columnhumidification region and a bubble column dehumidification region, anduse of the apparatus in various heat and mass exchange systems.

BACKGROUND

Fresh water shortages are becoming an increasing problem around theworld, with demand for fresh water for human consumption, irrigation,and/or industrial use continuing to grow. In order to meet the growingdemand for fresh water, various desalination methods may be used toproduce fresh water from salt-containing water such as seawater,brackish water, water produced from oil and/or gas extraction processes,flowback water, and/or wastewater. For example, one desalination methodis a humidification-dehumidification (HDH) process, which involvescontacting a saline solution with a carrier gas in a humidifier, suchthat the carrier gas becomes heated and humidified. The heated andhumidified gas is then brought into contact with cold water in adehumidifier, thereby producing pure water.

However, HDH systems and processes often involve certain drawbacks. Forexample, due to the use of a carrier gas in HDH systems, a largepercentage of non-condensable gas (e.g., air) is generally present,which can lead to relatively low heat and mass transfer rates. Inaddition, the presence of a non-condensable gas in a dehumidifier canincrease the thermal resistance to vapor condensation on a cold surface,thereby reducing the effectiveness of surface condensers. HDH systemsmay, additionally, require relatively large amounts of energy tooperate. HDH systems with improved properties such as, for example,reduced power consumption and/or increased heat and mass transfer ratesin the presence of non-condensable gases, are therefore desirable.

SUMMARY

Apparatuses comprising both a humidification region and adehumidification region, and use of the apparatuses in various heat andmass exchange systems, are disclosed. The subject matter of the presentinvention involves, in some cases, interrelated products, alternativesolutions to a particular problem, and/or a plurality of different usesof one or more systems and/or articles.

Certain embodiments relate to desalination systems. In some embodiments,a desalination system comprises a vessel comprising a humidificationregion comprising a humidification region liquid inlet fluidly connectedto a source of salt-containing water, a humidification region gas inletfluidly connected to a source of a gas, and a humidification region gasoutlet. In some embodiments, the humidification region is configured toproduce a vapor-containing humidification region gas outlet streamenriched in water vapor relative to the gas received from the gas inlet.In some cases, the vessel further comprises a dehumidification regioncomprising a dehumidification region gas inlet fluidly connected to thehumidification region gas outlet, a dehumidification region gas outlet,and a dehumidification region water outlet. In certain cases, thedehumidification region is configured to remove at least a portion ofthe water vapor from the vapor-containing humidification region gasoutlet stream to produce a dehumidification region water outlet streamand a dehumidification region gas outlet stream lean in water vaporrelative to the humidification region gas outlet stream.

In some embodiments, the desalination system comprises a vesselcomprising a humidification region comprising a humidification regiongas inlet fluidly connected to a source of a gas, a humidificationregion gas outlet, and at least one humidification chamber containing aliquid layer comprising an amount of salt-containing water. In somecases, the humidification region is configured to produce avapor-containing humidification region gas outlet stream enriched inwater vapor relative to the gas received from the gas inlet. In someembodiments, the vessel further comprises a dehumidification regioncomprising a dehumidification region gas inlet fluidly connected to thehumidification region gas outlet, a dehumidification region wateroutlet, and at least one dehumidification chamber containing a liquidlayer comprising an amount of water. In certain embodiments, thedehumidification region is configured to remove at least a portion ofthe water vapor from the humidification region gas outlet stream toproduce a dehumidification region water outlet stream and adehumidification region gas outlet stream lean in water vapor relativeto the humidification region gas outlet stream. In some cases, theliquid layer of the at least one humidification chamber and/or theliquid layer of the at least one dehumidification chamber have a heightof about 0.1 m or less.

In some embodiments, the desalination system comprises a vesselcomprising a humidification region comprising a humidification regionliquid inlet fluidly connected to a source of salt-containing water, ahumidification region gas inlet fluidly connected to a source of a gas,and a humidification region gas outlet. In some embodiments, thehumidification region is configured to produce a vapor-containinghumidification region gas outlet stream enriched in water vapor relativeto the gas received from the gas inlet. In some cases, the vesselfurther comprises a dehumidification region comprising adehumidification region gas inlet fluidly connected to thehumidification region gas outlet, a dehumidification region gas outlet,and a dehumidification region water outlet. In certain cases, thedehumidification region is configured to remove at least a portion ofthe water vapor from the vapor-containing humidification region gasoutlet stream to produce a dehumidification region water outlet streamand a dehumidification region gas outlet stream lean in water vaporrelative to the humidification region gas outlet stream. In someembodiments, the desalination system further comprises a heat exchangerseparate from the vessel. In certain cases, the heat exchanger isfluidly connected to the dehumidification region water outlet and thehumidification region liquid inlet. In certain embodiments, the heatexchanger is configured to transfer heat from the dehumidificationregion water outlet stream to the humidification region liquid inletstream.

According to some embodiments, the desalination system comprises avessel comprising a humidification region comprising a humidificationregion liquid inlet fluidly connected to a source of salt-containingwater, a humidification region gas inlet fluidly connected to a sourceof a gas, and a humidification region gas outlet. In some embodiments,the humidification region is configured to produce a vapor-containinghumidification region gas outlet stream enriched in water vapor relativeto the gas received from the gas inlet. In some cases, the vesselfurther comprises a dehumidification region comprising adehumidification region gas inlet fluidly connected to thehumidification region gas outlet, a dehumidification region gas outlet,and a dehumidification region water outlet. In certain cases, thedehumidification region is configured to remove at least a portion ofthe water vapor from the vapor-containing humidification region gasoutlet stream to produce a dehumidification region water outlet streamand a dehumidification region gas outlet stream lean in water vaporrelative to the humidification region gas outlet stream. In someembodiments, a portion of a gas stream is extracted from at least oneintermediate location in the humidification region and fed to at leastone intermediate location in the dehumidification region.

In some embodiments, the desalination system comprises a vesselcomprising a humidification region comprising a humidification regiongas inlet fluidly connected to a source of a gas, a humidificationregion gas outlet, and at least one humidification chamber containing aliquid layer comprising an amount of salt-containing water. In somecases, the humidification region is configured to produce avapor-containing humidification region gas outlet stream enriched inwater vapor relative to the gas received from the gas inlet. In someembodiments, the vessel further comprises a dehumidification regioncomprising a dehumidification region gas inlet fluidly connected to thehumidification region gas outlet, a dehumidification region wateroutlet, and at least one dehumidification chamber containing a liquidlayer comprising an amount of water. In certain embodiments, thedehumidification region is configured to remove at least a portion ofthe water vapor from the humidification region gas outlet stream toproduce a dehumidification region water outlet stream and adehumidification region gas outlet stream lean in water vapor relativeto the humidification region gas outlet stream. In some cases, the atleast one humidification chamber and/or the at least onedehumidification chamber are fluidly connected to one or more bubblegenerators.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control. If twoor more documents incorporated by reference include conflicting and/orinconsistent disclosure with respect to each other, then the documenthaving the later effective date shall control.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described byway of example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. In the figures,each identical or nearly identical component illustrated is typicallyrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Inthe figures:

FIG. 1A shows a schematic illustration of an exemplary desalinationsystem comprising a vessel comprising a single-stage humidificationregion and a single-stage dehumidification region, according to someembodiments;

FIG. 1B shows a schematic illustration of an exemplary desalinationsystem comprising a vessel comprising a single-stage humidificationregion, a single-stage dehumidification region, a stack, two dropleteliminators, and a liquid collector, according to some embodiments;

FIG. 2A shows, according to some embodiments, a schematic illustrationof an exemplary desalination system comprising a vessel comprising amulti-stage humidification region and a multi-stage dehumidificationregion;

FIG. 2B shows, according to some embodiments, a schematic illustrationof an exemplary desalination system comprising a vessel comprising amulti-stage humidification region, a multi-stage dehumidificationregion, and an intermediate gas injection point;

FIG. 2C shows, according to some embodiments, a schematic illustrationof an exemplary desalination system comprising a vessel comprising amulti-stage humidification region, a multi-stage dehumidificationregion, and an intermediate gas extraction point fluidly connected to anintermediate gas injection point;

FIG. 2D shows, according to some embodiments, a schematic illustrationof an exemplary desalination system comprising a vessel comprising amulti-stage humidification region, a multi-stage dehumidificationregion, two droplet eliminators, and a liquid collector;

FIG. 2E shows, according to some embodiments, a schematic illustrationof an exemplary desalination system comprising a vessel comprising amulti-stage humidification region, a multi-stage dehumidificationregion, two droplet eliminators, a liquid collector, and an externalsump;

FIG. 3 shows a schematic illustration of an exemplary desalinationsystem comprising a vessel comprising a humidification region comprisinga plurality of vertically-arranged stages positioned horizontallyadjacent to a dehumidification region comprising a plurality ofvertically-arranged stages, according to some embodiments;

FIG. 4 shows, according to some embodiments, a schematic illustration ofan exemplary desalination system comprising a vessel comprising ahumidification region comprising a plurality of horizontally-arrangedstages positioned horizontally adjacent to a dehumidification regioncomprising a plurality of horizontally-arranged stages;

FIG. 5 shows a schematic illustration of an exemplary desalinationsystem configured for batch processing, according to some embodiments;

FIG. 6A shows, according to some embodiments, a schematic illustrationof an exemplary baffle;

FIG. 6B shows, according to some embodiments, a schematic illustrationof an exemplary weaving baffle;

FIG. 7A shows a schematic diagram of an exemplary desalination systemcomprising a combined HDH apparatus and an external heat exchanger,according to some embodiments;

FIG. 7B shows a schematic diagram of an exemplary desalination systemcomprising a combined HDH apparatus, an external heat exchanger, anexternal cooling device, and an external heating device, according tosome embodiments;

FIG. 8 shows, according to some embodiments, a schematic illustration ofan exemplary desalination system comprising an apparatus comprising ahumidification region and a dehumidification region, a precipitationapparatus, a first heat exchanger, a second heating exchanger, and acooling device; and

FIG. 9 shows a schematic diagram, according to some embodiments, of anexemplary system comprising a pretreatment system, a desalinationsystem, and a precipitation apparatus.

DETAILED DESCRIPTION

Embodiments described herein generally relate to apparatuses thatinclude a vessel comprising a humidification region (e.g., a bubblecolumn humidification region) and a dehumidification region (e.g., abubble column dehumidification region), and associated systems andmethods. In certain embodiments, the apparatuses are configured toinclude various internal features, such as vapor distribution regionsand/or liquid flow control weirs and/or baffles. In some cases, theapparatuses described herein allow for simplified, lower cost systemswith improved performance (e.g., higher thermodynamic efficiency).According to some embodiments, the apparatuses may be used in waterpurification systems, such as desalination systems. The waterpurification systems may comprise additional devices external to theapparatuses, such as one or more heat exchangers, one or more heatingdevices, and/or one or more cooling devices.

While generally embodiments of the invention may employ a variety ofhumidifier and dehumidifier designs, including but not limited to thoseinvolving direct contact between gas and liquid phases, in someembodiments, bubble column humidifiers and bubble column dehumidifiersare described, which may be associated with certain advantages overcertain other types of humidifiers and dehumidifiers. For example,bubble column humidifiers and dehumidifiers may exhibit higherthermodynamic efficiency than certain other types of humidifiers (e.g.,packed bed humidifiers, spray towers, wetted wall towers) anddehumidifiers (e.g., surface condensers). Without wishing to be bound bya particular theory, the increased thermodynamic efficiency may be atleast partially attributed to the use of gas bubbles for heat and masstransfer in bubble column humidifiers and dehumidifiers, since gasbubbles may have more surface area available for heat and mass transferthan other types of surfaces (e.g., metallic tubes, liquid films,packing material). As described in further detail herein, a bubblecolumn humidifier and/or dehumidifier may have certain features thatfurther increase thermodynamic efficiency, including, but not limitedto, relatively low liquid level height, relatively high aspect ratioliquid flow paths, and multi-staged designs. As a result of theirincreased thermodynamic efficiency, bubble column humidifiers and/ordehumidifiers having a certain capacity may be reduced in size comparedto other types of humidifiers and/or dehumidifiers having the samecapacity. In a particular, non-limiting example, a bubble columnhumidifier having a height of 8 feet and a certain diameter may becapable of replacing two packed bed humidifier towers having a combinedheight of 25 feet and the same diameter.

It has been recognized within the context of this invention that it maybe advantageous to combine both a humidification region, for example abubble column humidification region, and a dehumidification region, forexample a bubble column dehumidification region, into a single vessel ofan apparatus. A vessel generally refers to any structure (e.g., a tank)capable of housing a humidification region and a dehumidificationregion. In some cases, a combined humidification-dehumidification (HDH)apparatus (e.g., an apparatus comprising a vessel comprising ahumidification region and a dehumidification region) may have fewercomponents and/or use less material than an HDH system comprising aseparate humidifier (e.g., a bubble column humidifier) and a separatedehumidifier (e.g., a bubble column dehumidifier). For example, an HDHsystem comprising a separate humidifier and dehumidifier may require oneor more ducts (e.g., for gas flow) and/or pipes (e.g., for liquid flow)connecting the humidifier and dehumidifier. In certain cases, the ductsand/or pipes may be expensive and/or burdensome to install. For example,in some industrial facilities (e.g., oil and gas facilities) that arelocated in remote areas, system components may be built off-site asdeployable skids. If a humidifier resides on one skid and a dehumidifierresides on another skid, ducting and/or piping connections may need tobe made during on-site installation, which may lengthen the timerequired for system deployment. In contrast, ducting and/or piping maybe reduced or eliminated in a combined HDH apparatus (e.g., a combinedbubble column apparatus). For example, a combined HDH apparatus mayeliminate the need for ducting between a humidifier gas outlet and adehumidifier gas inlet. To the extent that ducting is still required(e.g., between intermediate gas extraction inlets and outlets), the gasinlets and outlets may be positioned closer together, resulting in lessducting than in HDH systems comprising separate humidifiers anddehumidifiers. This may be advantageous, since ducting used to transportheated, humidified gas in an HDH system may be relatively expensive,large, heavy, and/or rigid. For example, one suitable type of ducting isstainless steel with fiberglass insulation, which is generally capableof accommodating high gas flow rates at high temperatures and/orwithstanding potentially corrosive environments. Installation of suchducting may be challenging due to its relatively large size, heavyweight, and/or high rigidity. Similarly, a combined HDH apparatus mayrequire less piping (e.g., for liquid flow) than an HDH systemcomprising separate humidifiers and dehumidifiers, since liquid inletsand outlets may be positioned in closer proximity to each other.

In addition to eliminated or reduced ducting and/or piping, a combinedHDH apparatus (e.g. combined bubble column apparatus) may haveadditional features that allow it to take up less space and/or use fewermaterials than an HDH system comprising a separate humidifier anddehumidifier. For example, a combined HDH apparatus may require lessspace for walkways and/or maintenance points since components may bepositioned closer together. In some cases, a combined HDH apparatus mayalso require less insulating material. For example, an HDH systemcomprising a separate humidifier and dehumidifier may have additionalwalls to be insulated compared to a combined HDH apparatus.

Other aspects of a combined HDH apparatus (e.g. combined bubble columnapparatus) may further reduce cost. For example, the humidification anddehumidification regions of a combined HDH apparatus may have structuralsimilarities, which may advantageously allow certain parts to be used inboth the humidification and dehumidification regions. Due to economiesof scale, a decrease in the number of unique parts in an HDH system mayadvantageously reduce the cost of the HDH system. Reducing the number ofunique parts may also simplify the production process.

According to some embodiments of the invention, an apparatus (e.g., acombined bubble column apparatus) comprises a vessel, and the vesselcomprises a humidification region (e.g., a bubble column humidificationregion) and a dehumidification region (e.g., a bubble columndehumidification region). The humidification region may be configured toreceive a humidification region gas inlet stream from a source of a gasvia at least one humidification region gas inlet. In some cases, the gascomprises at least one non-condensable gas. A non-condensable gasgenerally refers to a gas that cannot be condensed from gas phase toliquid phase under the operating conditions of the apparatus. Examplesof suitable non-condensable gases include, but are not limited to, air,nitrogen, oxygen, helium, argon, carbon monoxide, carbon dioxide, sulfuroxides (SO_(x)) (e.g., SO₂, SO₃), and/or nitrogen oxides (NO_(x)) (e.g.,NO, NO₂). In some embodiments, in addition to the at least onenon-condensable gas, the gas further comprises one or more additionalgases (e.g., the gas may be a gas mixture).

The humidification region may also be configured to receive ahumidification region liquid inlet stream (e.g., liquid feed stream)from a source of a liquid via at least one humidification region liquidinlet. In some embodiments, the liquid comprises a condensable fluid inliquid phase. A condensable fluid generally refers to a fluid that isable to condense from gas phase to liquid phase under the operatingconditions of the apparatus. Non-limiting, illustrative examples ofsuitable condensable fluids include water, ammonia, benzene, toluene,ethyl benzene, and/or alcohols. In addition to the condensable fluid inliquid phase, the liquid may further comprise one or more additionalliquids (e.g., the liquid may be a liquid mixture). In some embodiments,the liquid further comprises one or more contaminants. The one or morecontaminants may, for example, comprise one or more dissolved salts. Adissolved salt generally refers to a salt that has been solubilized tosuch an extent that the component ions (e.g., an anion, a cation) of thesalt are no longer ionically bonded to each other. Non-limiting examplesof dissolved salts that may be present in the liquid include sodiumchloride (NaCl), sodium bromide (NaBr), potassium chloride (KCl),potassium bromide (KBr), sodium carbonate (Na₂CO₃), sodium sulfate(Na₂SO₄), calcium chloride (CaCl₂), calcium sulfate (CaSO₄), magnesiumsulfate (MgSO₄), strontium sulfate (SrSO₄), barium sulfate (BaSO₄),barium-strontium sulfate (BaSr(SO₄)₂), iron (III) hydroxide (Fe(OH)₃),iron (III) carbonate (Fe₂(CO₃)₃), aluminum hydroxide (Al(OH)₃), aluminumcarbonate (Al₂(CO₃)₃), boron salts, and/or silicates. In a particularembodiment, the liquid comprises salt-containing water (e.g., watercomprising one or more dissolved salts). In certain cases, thesalt-containing water comprises seawater, brackish water, water producedform an oil and/or gas extraction process, flowback water, and/orwastewater (e.g., industrial wastewater). Non-limiting examples ofwastewater include textile mill wastewater, leather tannery wastewater,paper mill wastewater, cooling tower blowdown water, flue gasdesulfurization wastewater, landfill leachate water, and/or the effluentof a chemical process (e.g., the effluent of another desalination systemand/or chemical process).

In some embodiments, the humidification region liquid inlet stream has arelatively high concentration of one or more contaminants (e.g.,dissolved salts). In certain embodiments, the concentration of one ormore contaminants in the humidification region liquid inlet stream is atleast about 100 mg/L, at least about 200 mg/L, at least about 500 mg/L,at least about 1,000 mg/L, at least about 2,000 mg/L, at least about5,000 mg/L, at least about 10,000 mg/L, at least about 20,000 mg/L, atleast about 50,000 mg/L, at least about 75,000 mg/L, at least about100,000 mg/L, at least about 102,000 mg/L, at least about 110,000 mg/L,at least about 120,000 mg/L, at least about 150,000 mg/L, at least about175,000 mg/L, at least about 200,000 mg/L, at least about 210,000 mg/L,at least about 219,000 mg/L, at least about 220,000 mg/L, at least about250,000 mg/L, at least about 275,000 mg/L, at least about 300,000 mg/L,at least about 310,000 mg/L, at least about 312,000 mg/L, at least about320,000 mg/L, at least about 350,000 mg/L, or at least about 375,000mg/L (and/or, in certain embodiments, up to the solubility limit of theone or more contaminants in the liquid stream). In some embodiments, theconcentration of one or more contaminants in the humidification regionliquid inlet stream is in the range of about 100 mg/L to about 375,000mg/L, about 1,000 mg/L to about 10,000 mg/L, about 1,000 mg/L to about50,000 mg/L, about 1,000 mg/L to about 75,000 mg/L, about 1,000 mg/L toabout 100,000 mg/L, about 1,000 mg/L to about 150,000 mg/L, about 1,000mg/L to about 200,000 mg/L, about 1,000 mg/L to about 250,000 mg/L,about 1,000 mg/L to about 300,000 mg/L, about 1,000 mg/L to about350,000 mg/L, about 1,000 mg/L to about 375,000 mg/L, about 10,000 mg/Lto about 50,000 mg/L, about 10,000 mg/L to about 75,000 mg/L, about10,000 mg/L to about 100,000 mg/L, about 10,000 mg/L to about 150,000mg/L, about 10,000 mg/L to about 200,000 mg/L, about 10,000 mg/L toabout 250,000 mg/L, about 10,000 mg/L to about 300,000 mg/L, about10,000 mg/L to about 350,000 mg/L, about 10,000 mg/L to about 375,000mg/L, about 50,000 mg/L to about 100,000 mg/L, about 50,000 mg/L toabout 150,000 mg/L, about 50,000 mg/L to about 200,000 mg/L, about50,000 mg/L to about 250,000 mg/L, about 50,000 mg/L to about 300,000mg/L, about 50,000 mg/L to about 350,000 mg/L, about 50,000 mg/L toabout 375,000 mg/L, about 100,000 mg/L to about 150,000 mg/L, about100,000 mg/L to about 200,000 mg/L, about 100,000 mg/L to about 250,000mg/L, about 100,000 mg/L to about 300,000 mg/L, about 100,000 mg/L toabout 350,000 mg/L, about 100,000 mg/L to about 375,000 mg/L, about102,000 mg/L to about 219,000 mg/L, about 102,000 mg/L to about 312,000mg/L, about 150,000 mg/L to about 200,000 mg/L, about 150,000 mg/L toabout 250,000 mg/L, about 150,000 mg/L to about 300,000 mg/L, about150,000 mg/L to about 350,000 mg/L, about 150,000 mg/L to about 375,000mg/L, about 200,000 mg/L to about 250,000 mg/L, about 200,000 mg/L toabout 300,000 mg/L, about 200,000 mg/L to about 350,000 mg/L, about200,000 mg/L to about 375,000 mg/L, about 250,000 mg/L to about 300,000mg/L, about 250,000 mg/L to about 350,000 mg/L, about 250,000 mg/L toabout 375,000 mg/L, about 300,000 mg/L to about 350,000 mg/L, or about300,000 mg/L to about 375,000 mg/L. As noted above, the one or morecontaminants may comprise one or more dissolved salts (e.g., NaCl). Theconcentration of a dissolved salt generally refers to the combinedconcentrations of the cation and the anion of the salt. For example, theconcentration of dissolved NaCl would refer to the sum of theconcentration of sodium ions (Na⁺) and the concentration of chlorideions (Cl⁻). The concentration of a contaminant (e.g., a dissolved salt)may be measured according to any method known in the art. For example,methods for measuring the concentration of a contaminant includeinductively coupled plasma (ICP) spectroscopy (e.g., inductively coupledplasma optical emission spectroscopy). As one non-limiting example, anOptima 8300 ICP-OES spectrometer may be used.

In some embodiments, the humidification region liquid inlet streamcontains at least one contaminant (e.g., dissolved salt) in an amount ofat least about 1 wt %, at least about 5 wt %, at least about 10 wt %, atleast about 15 wt %, at least about 20 wt %, at least about 25 wt %, atleast about 26 wt %, at least about 27 wt %, at least about 28 wt %, atleast about 29 wt %, or at least about 30 wt % (and/or, in certainembodiments, up to the solubility limit of the at least one contaminantin the liquid stream). In some embodiments, the humidification regionliquid inlet stream comprises at least one contaminant in an amount inthe range of about 1 wt % to about 10 wt %, about 1 wt % to about 20 wt%, about 1 wt % to about 25 wt %, about 1 wt % to about 26 wt %, about 1wt % to about 27 wt %, about 1 wt % to about 28 wt %, about 1 wt % toabout 29 wt %, about 1 wt % to about 30 wt %, about 10 wt % to about 20wt %, about 10 wt % to about 25 wt %, about 10 wt % to about 26 wt %,about 10 wt % to about 27 wt %, about 10 wt % to about 28 wt %, about 10wt % to about 29 wt %, about 10 wt % to about 30 wt %, about 20 wt % toabout 25 wt %, about 20 wt % to about 26 wt %, about 20 wt % to about 27wt %, about 20 wt % to about 28 wt %, about 20 wt % to about 29 wt %,about 20 wt % to about 30 wt %, about 25 wt % to about 26 wt %, about 25wt % to about 27 wt %, about 25 wt % to about 28 wt %, about 25 wt % toabout 29 wt %, or about 25 wt % to about 30 wt %.

According to some embodiments, the humidification region liquid inletstream has a relatively high total contaminant concentration (e.g.,concentration of all contaminants present in the liquid stream). Incertain cases, the total contaminant concentration of the humidificationregion liquid inlet stream is at least about 1,000 mg/L, at least about2,000 mg/L, at least about 5,000 mg/L, at least about 10,000 mg/L, atleast about 20,000 mg/L, at least about 50,000 mg/L, at least about75,000 mg/L, at least about 100,000 mg/L, at least about 110,000 mg/L,at least about 120,000 mg/L, at least about 150,000 mg/L, at least about175,000 mg/L, at least about 200,000 mg/L, at least about 210,000 mg/L,at least about 220,000 mg/L, at least about 250,000 mg/L, at least about275,000 mg/L, at least about 300,000 mg/L, at least about 310,000 mg/L,at least about 320,000 mg/L, at least about 350,000 mg/L, at least about375,000 mg/L, at least about 400,000 mg/L, at least about 450,000 mg/L,or at least about 500,000 mg/L (and/or, in certain embodiments, up tothe solubility limit of the dissolved contaminant(s) in the liquidstream). In some embodiments, the total contaminant concentration of thehumidification region liquid inlet stream is in the range of about 1,000mg/L to about 10,000 mg/L, about 1,000 mg/L to about 20,000 mg/L, about1,000 mg/L to about 50,000 mg/L, about 1,000 mg/L to about 75,000 mg/L,about 1,000 mg/L to about 100,000 mg/L, about 1,000 mg/L to about150,000 mg/L, about 1,000 mg/L to about 200,000 mg/L, about 1,000 mg/Lto about 250,000 mg/L, about 1,000 mg/L to about 300,000 mg/L, about1,000 mg/L to about 350,000 mg/L, about 1,000 mg/L to about 400,000mg/L, about 1,000 mg/L to about 450,000 mg/L, about 1,000 mg/L to about500,000 mg/L, about 10,000 mg/L to about 20,000 mg/L, about 10,000 mg/Lto about 50,000 mg/L, about 10,000 mg/L to about 75,000 mg/L, about10,000 mg/L to about 100,000 mg/L, about 10,000 mg/L to about 150,000mg/L, about 10,000 mg/L to about 200,000 mg/L, about 10,000 mg/L toabout 250,000 mg/L, about 10,000 mg/L to about 300,000 mg/L, about10,000 mg/L to about 350,000 mg/L, about 10,000 mg/L to about 400,000mg/L, about 10,000 mg/L to about 450,000 mg/L, about 10,000 mg/L toabout 500,000 mg/L, about 20,000 mg/L to about 50,000 mg/L, about 20,000mg/L to about 75,000 mg/L, about 20,000 mg/L to about 100,000 mg/L,about 20,000 mg/L to about 150,000 mg/L, about 20,000 mg/L to about200,000 mg/L, about 20,000 mg/L to about 250,000 mg/L, about 20,000 mg/Lto about 300,000 mg/L, about 20,000 mg/L to about 350,000 mg/L, about20,000 mg/L to about 400,000 mg/L, about 20,000 mg/L to about 450,000mg/L, about 20,000 mg/L to about 500,000 mg/L, about 50,000 mg/L toabout 100,000 mg/L, about 50,000 mg/L to about 150,000 mg/L, about50,000 mg/L to about 200,000 mg/L, about 50,000 mg/L to about 250,000mg/L, about 50,000 mg/L to about 300,000 mg/L, about 50,000 mg/L toabout 350,000 mg/L, about 50,000 mg/L to about 400,000 mg/L, about50,000 mg/L to about 450,000 mg/L, about 50,000 mg/L to about 500,000mg/L, about 100,000 mg/L to about 150,000 mg/L, about 100,000 mg/L toabout 200,000 mg/L, about 100,000 mg/L to about 250,000 mg/L, about100,000 mg/L to about 300,000 mg/L, about 100,000 mg/L to about 350,000mg/L, about 100,000 mg/L to about 400,000 mg/L, about 100,000 mg/L toabout 450,000 mg/L, or about 100,000 mg/L to about 500,000 mg/L.

In some embodiments, the contaminants present in the humidificationregion liquid inlet stream comprise two or more dissolved salts. Theconcentration of a plurality of dissolved salts generally refers to thecombined concentrations of all the cations and anions of the dissolvedsalts. As a simple, non-limiting example, in a liquid stream comprisingdissolved NaCl and dissolved MgSO₄, the total dissolved saltconcentration would refer to the sum of the concentrations of the Na⁺,Cl⁻, Me²⁺, and SO₄ ²⁻ ions. The total contaminant concentration may bemeasured according to any method known in the art. For example, anon-limiting example of a suitable method for measuring totalcontaminant concentration is the SM 2540C method. According to the SM2540C method, a sample comprising an amount of liquid comprising one ormore dissolved solids is filtered (e.g., through a glass fiber filter),and the filtrate is evaporated to dryness in a weighed dish at 180° C.The increase in dish weight represents the mass of the total dissolvedsolids in the sample. The total contaminant concentration of the samplemay be obtained by dividing the mass of the total dissolved solids bythe volume of the original sample.

In some embodiments, the humidification region liquid inlet stream has atotal contaminant concentration of at least about 1 wt %, at least about5 wt %, at least about 10 wt %, at least about 15 wt %, at least about20 wt %, at least about 25 wt %, at least about 26 wt %, at least about27 wt %, at least about 28 wt %, at least about 29 wt %, or at leastabout 30 wt % (and/or, in certain embodiments, up to the solubilitylimit of the dissolved contaminant(s) in the liquid stream). In someembodiments, the humidification region liquid inlet stream has a totalcontaminant concentration in the range of about 1 wt % to about 10 wt %,about 1 wt % to about 20 wt %, about 1 wt % to about 25 wt %, about 1 wt% to about 26 wt %, about 1 wt % to about 27 wt %, about 1 wt % to about28 wt %, about 1 wt % to about 29 wt %, about 1 wt % to about 30 wt %,about 10 wt % to about 20 wt %, about 10 wt % to about 25 wt %, about 10wt % to about 26 wt %, about 10 wt % to about 27 wt %, about 10 wt % toabout 28 wt %, about 10 wt % to about 29 wt %, about 10 wt % to about 30wt %, about 20 wt % to about 25 wt %, about 20 wt % to about 26 wt %,about 20 wt % to about 27 wt %, about 20 wt % to about 28 wt %, about 20wt % to about 29 wt %, about 20 wt % to about 30 wt %, about 25 wt % toabout 26 wt %, about 25 wt % to about 27 wt %, about 25 wt % to about 28wt %, about 25 wt % to about 29 wt %, or about 25 wt % to about 30 wt %.

In the humidification region, the gas may come into contact (e.g.,direct or indirect contact) with the liquid. In some embodiments, thetemperature of the liquid is higher than the temperature of the gas, andupon contact of the gas and the liquid, heat and/or mass may betransferred from the liquid to the gas. According to certainembodiments, at least a portion of the condensable fluid in the liquidis transferred to the gas via an evaporation (e.g., humidification)process, thereby producing a vapor-containing humidification region gasoutlet stream (e.g., an at least partially humidified gas stream) and ahumidification region liquid outlet stream. In some embodiments, thehumidification region gas outlet stream comprises a vapor mixture (e.g.,a mixture of the condensable fluid in vapor phase and thenon-condensable gas). In certain cases, the condensable fluid is water,and the humidification region gas outlet stream is enriched in watervapor relative to the gas received from the humidification region gasinlet. In some embodiments, the humidification region liquid outletstream has a higher concentration of one or more contaminants (e.g.,dissolved salts) than the humidification region liquid inlet stream(e.g., the humidification region liquid outlet stream is enriched in theone or more contaminants relative to the humidification region liquidinlet stream).

According to some embodiments, the humidification region liquid outletstream has a relatively high concentration of one or more contaminants(e.g., dissolved salts). In certain embodiments, the concentration ofone or more contaminants in the humidification region liquid outletstream is at least about 100 mg/L, at least about 200 mg/L, at leastabout 500 mg/L, at least about 1,000 mg/L, at least about 2,000 mg/L, atleast about 5,000 mg/L, at least about 10,000 mg/L, at least about20,000 mg/L, at least about 50,000 mg/L, at least about 75,000 mg/L, atleast about 100,000 mg/L, at least about 150,000 mg/L, at least about200,000 mg/L, at least about 250,000 mg/L, at least about 300,000 mg/L,at least about 350,000 mg/L, at least about 400,000 mg/L, at least about450,000 mg/L, or at least about 500,000 mg/L (and/or, in certainembodiments, up to the solubility limit of the one or more contaminantsin the liquid stream). In some embodiments, the concentration of one ormore contaminants in the humidification region liquid outlet stream isin the range of about 1,000 mg/L to about 10,000 mg/L, about 1,000 mg/Lto about 20,000 mg/L, about 1,000 mg/L to about 50,000 mg/L, about 1,000mg/L to about 100,000 mg/L, about 1,000 mg/L to about 150,000 mg/L,about 1,000 mg/L to about 200,000 mg/L, about 1,000 mg/L to about250,000 mg/L, about 1,000 mg/L to about 300,000 mg/L, about 1,000 mg/Lto about 350,000 mg/L, about 1,000 mg/L to about 400,000 mg/L, about1,000 mg/L to about 450,000 mg/L, about 1,000 mg/L to about 500,000mg/L, about 10,000 mg/L to about 20,000 mg/L, about 10,000 mg/L to about50,000 mg/L, about 10,000 mg/L to about 100,000 mg/L, about 10,000 mg/Lto about 150,000 mg/L, about 10,000 mg/L to about 200,000 mg/L, about10,000 mg/L to about 250,000 mg/L, about 10,000 mg/L to about 300,000mg/L, about 10,000 mg/L to about 350,000 mg/L, about 10,000 mg/L toabout 400,000 mg/L, about 10,000 mg/L to about 450,000 mg/L, about10,000 mg/L to about 500,000 mg/L, about 20,000 mg/L to about 50,000mg/L, about 20,000 mg/L to about 100,000 mg/L, about 20,000 mg/L toabout 150,000 mg/L, about 20,000 mg/L to about 200,000 mg/L, about20,000 mg/L to about 250,000 mg/L, about 20,000 mg/L to about 300,000mg/L, about 20,000 mg/L to about 350,000 mg/L, about 20,000 mg/L toabout 400,000 mg/L, about 20,000 mg/L to about 450,000 mg/L, about20,000 mg/L to about 500,000 mg/L, about 50,000 mg/L to about 100,000mg/L, about 50,000 mg/L to about 150,000 mg/L, about 50,000 mg/L toabout 200,000 mg/L, about 50,000 mg/L to about 250,000 mg/L, about50,000 mg/L to about 300,000 mg/L, about 50,000 mg/L to about 350,000mg/L, about 50,000 mg/L to about 400,000 mg/L, about 50,000 mg/L toabout 450,000 mg/L, about 50,000 mg/L to about 500,000 mg/L, about100,000 mg/L to about 150,000 mg/L, about 100,000 mg/L to about 200,000mg/L, about 100,000 mg/L to about 250,000 mg/L, about 100,000 mg/L toabout 300,000 mg/L, about 100,000 mg/L to about 350,000 mg/L, about100,000 mg/L to about 400,000 mg/L, about 100,000 mg/L to about 450,000mg/L, or about 100,000 mg/L to about 500,000 mg/L.

In some embodiments, the humidification region liquid outlet streamcontains at least one contaminant (e.g., dissolved salt) in an amount ofat least about 1 wt %, at least about 5 wt %, at least about 10 wt %, atleast about 15 wt %, at least about 20 wt %, at least about 25 wt %, atleast about 26 wt %, at least about 27 wt %, at least about 28 wt %, atleast about 29 wt %, or at least about 30 wt % (and/or, in certainembodiments, up to the solubility limit of the contaminant in the liquidstream). In some embodiments, the humidification region liquid outletstream comprises at least one contaminant in an amount in the range ofabout 1 wt % to about 10 wt %, about 1 wt % to about 20 wt %, about 1 wt% to about 25 wt %, about 1 wt % to about 26 wt %, about 1 wt % to about27 wt %, about 1 wt % to about 28 wt %, about 1 wt % to about 29 wt %,about 1 wt % to about 30 wt %, about 10 wt % to about 20 wt %, about 10wt % to about 25 wt %, about 10 wt % to about 26 wt %, about 10 wt % toabout 27 wt %, about 10 wt % to about 28 wt %, about 10 wt % to about 29wt %, about 10 wt % to about 30 wt %, about 20 wt % to about 25 wt %,about 20 wt % to about 26 wt %, about 20 wt % to about 27 wt %, about 20wt % to about 28 wt %, about 20 wt % to about 29 wt %, about 20 wt % toabout 30 wt %, about 25 wt % to about 26 wt %, about 25 wt % to about 27wt %, about 25 wt % to about 28 wt %, about 25 wt % to about 29 wt %, orabout 25 wt % to about 30 wt %.

In some embodiments, the concentration of one or more contaminants inthe humidification region liquid outlet stream is substantially greaterthan the concentration of the one or more contaminants in thehumidification region liquid inlet stream (e.g., liquid feed stream)received by the apparatus. In some cases, the concentration of one ormore contaminants in the humidification region liquid outlet stream isat least about 0.5%, about 1%, about 2%, about 5%, about 10%, about 15%,or about 20% greater than the concentration of the one or morecontaminants in the humidification region liquid inlet stream.

According to some embodiments, the humidification region liquid outletstream has a relatively high total contaminant concentration (e.g.,concentration of all contaminants present in the liquid stream). Incertain cases, the humidification region liquid outlet stream has atotal contaminant concentration of at least about 1,000 mg/L, at leastabout 2,000 mg/L, at least about 5,000 mg/L, at least about 10,000 mg/L,at least about 20,000 mg/L, at least about 50,000 mg/L, at least about75,000 mg/L, at least about 100,000 mg/L, at least about 150,000 mg/L,at least about 200,000 mg/L, at least about 250,000 mg/L, at least about300,000 mg/L, at least about 350,000 mg/L, at least about 400,000 mg/L,at least about 450,000 mg/L, at least about 500,000 mg/L, at least about550,000 mg/L, or at least about 600,000 mg/L (and/or, in certainembodiments, up to the solubility limit of the contaminant(s) in theliquid stream). In some embodiments, the total contaminant concentrationof the humidification region liquid outlet stream is in the range ofabout 10,000 mg/L to about 20,000 mg/L, about 10,000 mg/L to about50,000 mg/L, about 10,000 mg/L to about 100,000 mg/L, about 10,000 mg/Lto about 150,000 mg/L, about 10,000 mg/L to about 200,000 mg/L, about10,000 mg/L to about 250,000 mg/L, about 10,000 mg/L to about 300,000mg/L, about 10,000 mg/L to about 350,000 mg/L, about 10,000 mg/L toabout 400,000 mg/L, about 10,000 mg/L to about 450,000 mg/L, about10,000 mg/L to about 500,000 mg/L, about 10,000 mg/L to about 550,000mg/L, about 10,000 mg/L to about 600,000 mg/L, about 20,000 mg/L toabout 50,000 mg/L, about 20,000 mg/L to about 100,000 mg/L, about 20,000mg/L to about 150,000 mg/L, about 20,000 mg/L to about 200,000 mg/L,about 20,000 mg/L to about 250,000 mg/L, about 20,000 mg/L to about300,000 mg/L, about 20,000 mg/L to about 350,000 mg/L, about 20,000 mg/Lto about 400,000 mg/L, about 20,000 mg/L to about 450,000 mg/L, about20,000 mg/L to about 500,000 mg/L, about 20,000 mg/L to about 550,000mg/L, about 20,000 mg/L to about 600,000 mg/L, about 50,000 mg/L toabout 100,000 mg/L, about 50,000 mg/L to about 150,000 mg/L, about50,000 mg/L to about 200,000 mg/L, about 50,000 mg/L to about 250,000mg/L, about 50,000 mg/L to about 300,000 mg/L, about 50,000 mg/L toabout 350,000 mg/L, about 50,000 mg/L to about 400,000 mg/L, about50,000 mg/L to about 450,000 mg/L, about 50,000 mg/L to about 500,000mg/L, about 50,000 mg/L to about 550,000 mg/L, about 50,000 mg/L toabout 600,000 mg/L, about 100,000 mg/L to about 200,000 mg/L, about100,000 mg/L to about 250,000 mg/L, about 100,000 mg/L to about 300,000mg/L, about 100,000 mg/L to about 350,000 mg/L, about 100,000 mg/L toabout 400,000 mg/L, about 100,000 mg/L to about 450,000 mg/L, about100,000 mg/L to about 500,000 mg/L, about 100,000 mg/L to about 550,000mg/L, or about 100,000 mg/L to about 600,000 mg/L.

In some embodiments, the humidification region liquid outlet stream hasa total contaminant concentration of at least about 10 wt %, at leastabout 15 wt %, at least about 20 wt %, at least about 25 wt %, at leastabout 26 wt %, at least about 27 wt %, at least about 28 wt %, at leastabout 29 wt %, or at least about 30 wt % (and/or, in certainembodiments, up to the solubility limit of the contaminant(s) in theliquid stream). In some embodiments, the humidification region liquidoutlet stream has a total contaminant concentration in the range ofabout 10 wt % to about 20 wt %, about 10 wt % to about 25 wt %, about 10wt % to about 26 wt %, about 10 wt % to about 27 wt %, about 10 wt % toabout 28 wt %, about 10 wt % to about 29 wt %, about 10 wt % to about 30wt %, about 20 wt % to about 25 wt %, about 20 wt % to about 26 wt %,about 20 wt % to about 27 wt %, about 20 wt % to about 28 wt %, about 20wt % to about 29 wt %, about 20 wt % to about 30 wt %, about 25 wt % toabout 26 wt %, about 25 wt % to about 27 wt %, about 25 wt % to about 28wt %, about 25 wt % to about 29 wt %, or about 25 wt % to about 30 wt %.

In some embodiments, the humidification region liquid outlet stream hasa substantially greater total contaminant concentration than thehumidification region liquid inlet stream (e.g., liquid feed stream)received by the apparatus. In some cases, the total contaminantconcentration of the humidification region liquid outlet stream is atleast about 5%, at least about 6%, at least about 10%, at least about14%, at least about 15%, at least about 20%, or at least about 25%greater than the total contaminant concentration of the humidificationregion liquid inlet stream. In some embodiments, the humidificationregion is configured such that a liquid inlet is positioned at a firstend (e.g., a top end) of the humidification region, and a gas inlet ispositioned at a second, opposite end (e.g., a bottom end) of thehumidification region. Such a configuration may facilitate the flow of aliquid stream in a first direction (e.g., downwards) through thehumidification region and the flow of a gas stream in a second,substantially opposite direction (e.g., upwards) through thehumidification region, which may advantageously result in high thermalefficiency.

In some embodiments, the dehumidification region of the vessel of thecombined HDH apparatus (e.g., combined bubble column apparatus) isconfigured to receive the humidification region gas outlet stream (e.g.,a heated, at least partially humidified gas stream) via at least onedehumidification region gas inlet as a dehumidification region gas inletstream. The dehumidification region may also be configured to receive adehumidification region liquid inlet stream via at least onedehumidification region liquid inlet. According to some embodiments, thedehumidification region liquid inlet stream comprises the condensablefluid in liquid phase. In some embodiments, for example, thedehumidification region liquid inlet stream comprises water. In certaincases, the dehumidification region liquid inlet stream comprisessubstantially pure water (e.g., water having a relatively low level ofcontaminants).

In the dehumidification region, the dehumidification region gas inletstream (e.g., the heated, at least partially humidified humidificationregion gas outlet stream) may come into contact (e.g., direct orindirect contact) with the dehumidification region liquid inlet stream.The dehumidification region gas inlet stream may have a highertemperature than the dehumidification region liquid inlet stream, andupon contact of the gas and liquid streams, heat and/or mass may betransferred from the dehumidification region gas inlet stream to thedehumidification region liquid inlet stream. In certain embodiments, thedehumidification region gas inlet stream comprises the condensable fluidin vapor phase and the non-condensable gas, and at least a portion ofthe condensable fluid is transferred from the dehumidification regiongas inlet stream to the dehumidification region liquid inlet stream viaa condensation (e.g., dehumidification) process, thereby producing adehumidification region liquid outlet stream comprising the condensablefluid in liquid phase and an at least partially dehumidifieddehumidification region gas outlet stream. In certain cases, thecondensable fluid is water, and the dehumidification region gas outletstream is lean in water vapor relative to the dehumidification regiongas inlet stream (e.g., humidification region gas outlet stream). Insome embodiments, the dehumidification region liquid outlet streamcomprises substantially pure water. In certain cases, thedehumidification region liquid outlet stream comprises water in theamount of at least about 95 wt %, at least about 99 wt %, at least about99.9 wt %, or at least about 99.99 wt % (and/or, in certain embodiments,up to about 99.999 wt %, or more).

According to some embodiments, the dehumidification region liquid outletstream has a relatively low concentration of one or more contaminants(e.g., dissolved salts). In certain embodiments, the concentration ofone or more contaminants in the dehumidification region liquid outletstream is about 500 mg/L or less, about 200 mg/L or less, about 100 mg/Lor less, about 50 mg/L or less, about 20 mg/L or less, about 10 mg/L orless, about 5 mg/L or less, about 2 mg/L or less, about 1 mg/L or less,about 0.5 mg/L or less, about 0.2 mg/L or less, about 0.1 mg/L or less,about 0.05 mg/L or less, about 0.02 mg/L or less, or about 0.01 mg/L orless. In some cases, the concentration of one or more contaminants inthe dehumidification region liquid outlet stream is substantially zero(e.g., not detectable). In certain cases, the concentration of one ormore contaminants in the dehumidification region liquid outlet stream isin the range of about 0 mg/L to about 500 mg/L, about 0 mg/L to about200 mg/L, about 0 mg/L to about 100 mg/L, about 0 mg/L to about 50 mg/L,about 0 mg/L to about 20 mg/L, about 0 mg/L to about 10 mg/L, about 0mg/L to about 5 mg/L, about 0 mg/L to about 2 mg/L, about 0 mg/L toabout 1 mg/L, about 0 mg/L to about 0.5 mg/L, about 0 mg/L to about 0.1mg/L, about 0 mg/L to about 0.05 mg/L, about 0 mg/L to about 0.02 mg/L,or about 0 mg/L to about 0.01 mg/L.

In some embodiments, the dehumidification region liquid outlet streamcontains one or more contaminants in an amount of about 2 wt % or less,about 1 wt % or less, about 0.5 wt % or less, about 0.2 wt % or less,about 0.1 wt % or less, about 0.05 wt % or less, or about 0.01 wt % orless. In some embodiments, the dehumidification region liquid outletstream contains one or more contaminants in an amount in the range ofabout 0.01 wt % to about 2 wt %, about 0.01 wt % to about 1 wt %, about0.01 wt % to about 0.5 wt %, about 0.01 wt % to about 0.2 wt %, or about0.01 wt % to about 0.1 wt %.

In some embodiments, the concentration of one or more contaminants inthe dehumidification region liquid outlet stream is substantially lessthan the concentration of the one or more contaminants in thehumidification region liquid inlet stream (e.g., liquid feed stream)received by the apparatus. In some cases, the concentration of one ormore contaminants in the dehumidification region liquid outlet stream isat least about 0.5%, about 1%, about 2%, about 5%, about 10%, about 15%,or about 20% less than the concentration of the one or more contaminantsin the humidification region liquid inlet stream.

According to some embodiments, the dehumidification region liquid outletstream has a relatively low total contaminant concentration (e.g.,concentration of all contaminants present in the liquid stream). Incertain cases, the dehumidification region liquid outlet stream has atotal contaminant concentration of about 500 mg/L or less, about 200mg/L or less, about 100 mg/L or less, about 50 mg/L or less, about 20mg/L or less, about 10 mg/L or less, about 5 mg/L or less, about 2 mg/Lor less, about 1 mg/L or less, about 0.5 mg/L or less, about 0.2 mg/L orless, about 0.1 mg/L or less, about 0.05 mg/L or less, about 0.02 mg/Lor less, or about 0.01 mg/L or less. In some cases, the totalcontaminant concentration of the dehumidification region liquid outletstream is substantially zero (e.g., not detectable). In certainembodiments, the total contaminant concentration of the dehumidificationregion liquid outlet stream is in the range of about 0 mg/L to about 500mg/L, about 0 mg/L to about 200 mg/L, about 0 mg/L to about 100 mg/L,about 0 mg/L to about 50 mg/L, about 0 mg/L to about 20 mg/L, about 0mg/L to about 10 mg/L, about 0 mg/L to about 5 mg/L, about 0 mg/L toabout 2 mg/L, about 0 mg/L to about 1 mg/L, about 0 mg/L to about 0.5mg/L, about 0 mg/L to about 0.2 mg/L, about 0 mg/L to about 0.1 mg/L,about 0 mg/L to about 0.05 mg/L, about 0 mg/L to about 0.02 mg/L, orabout 0 mg/L to about 0.01 mg/L.

In some embodiments, the dehumidification region liquid outlet streamcontains a total amount of contaminants of about 5 wt % or less, about 2wt % or less, about 1 wt % or less, about 0.5 wt % or less, about 0.2 wt% or less, about 0.1 wt % or less, about 0.05 wt % or less, or about0.01 wt % or less. In some embodiments, the dehumidification regionliquid outlet stream contains a total amount of contaminants in therange of about 0.01 wt % to about 5 wt %, about 0.01 wt % to about 2 wt%, about 0.01 wt % to about 1 wt %, about 0.01 wt % to about 0.5 wt %,about 0.01 wt % to about 0.2 wt %, or about 0.01 wt % to about 0.1 wt %.

In some embodiments, the total contaminant concentration of thedehumidification region liquid outlet stream is substantially less thanthe total contaminant concentration of the humidification region liquidinlet stream (e.g., liquid feed stream) received by the apparatus. Insome cases, the total contaminant concentration of the dehumidificationregion liquid outlet stream is at least about 0.5%, about 1%, about 2%,about 5%, about 10%, about 15%, or about 20% less than the totalcontaminant concentration of the humidification region liquid inletstream.

In some embodiments, the dehumidification region is configured such thata liquid inlet is positioned at a first end (e.g., a top end) of thedehumidification region, and a gas inlet is positioned at a second,opposite end (e.g., a bottom end) of the dehumidification region. Such aconfiguration may facilitate the flow of a liquid stream in a firstdirection (e.g., downwards) through the dehumidification region and theflow of a gas stream in a second, substantially opposite direction(e.g., upwards) through the dehumidification region, which mayadvantageously result in high thermal efficiency.

According to some embodiments, the humidification region is a bubblecolumn humidification region. In certain cases, the bubble columnhumidification region comprises at least one stage comprising a chamber.The chamber may, according to some embodiments, comprise a liquid layerand a vapor distribution region (e.g., positioned above the liquidlayer). The vapor distribution region refers to the space within thechamber (e.g., the portion of the chamber not occupied by the liquidlayer) throughout which vapor is distributed. In some cases, the liquidlayer comprises a condensable fluid in liquid phase (e.g., water) andone or more contaminants (e.g., dissolved salts). The chamber may alsobe in fluid communication with a bubble generator, which may act as agas inlet for the at least one stage of the humidification region.

In some embodiments, the dehumidification region is a bubble columndehumidification region. In certain cases, the bubble columndehumidification region comprises at least one stage comprising achamber. The chamber may, according to some embodiments, comprise aliquid layer and a vapor distribution region (e.g., positioned above theliquid layer). In some cases, the liquid layer comprises the condensablefluid in liquid phase. The chamber may also be in fluid communicationwith a bubble generator, which may act as a gas inlet for the at leastone stage of the dehumidification region.

In certain cases, the combined HDH apparatus is a combined bubble columnapparatus that further comprises a gas distribution chamber. In someembodiments, the gas distribution chamber comprises an apparatus gasinlet fluidly connected to a source of a gas (e.g., a non-condensablegas). The gas distribution chamber may comprise a gas distributionregion, which may have sufficient volume to allow the gas tosubstantially evenly diffuse over the cross section of the combinedbubble column apparatus. The gas distribution region refers to the spacewithin the gas distribution chamber throughout which gas is distributed.In some cases, the gas distribution chamber further comprises a liquidlayer (e.g., a liquid sump volume). For example, liquid (e.g.,comprising the condensable fluid in liquid phase and one or morecontaminants) may collect in the sump volume after exiting thehumidification region. In some cases, the liquid sump volume is indirect contact with a liquid outlet of the combined bubble columnapparatus (e.g., a humidification region liquid outlet). In certainembodiments, the liquid sump volume is in fluid communication with apump that pumps liquid out of the combined bubble column apparatus. Theliquid sump volume may, for example, provide a positive suction pressureon the intake of the pump, and may advantageously prevent negative(e.g., vacuum) suction pressure that could induce deleterious cavitationbubbles. In some cases, the liquid sump volume may advantageouslydecrease the sensitivity of the bubble column apparatus to suddenchanges in heat transfer rates (e.g., due to intermittent feeding ofsalt-containing water to and/or intermittent discharge of pure waterfrom the apparatus). In certain embodiments, such as those embodimentsin which at least the humidification region of the combined bubblecolumn apparatus comprises a plurality of vertically-arranged stages,the gas distribution chamber is positioned at or near the bottom portionof the combined bubble column apparatus (e.g., below the humidificationregion).

In some embodiments, a humidification region gas inlet stream comprisingthe gas (e.g., the non-condensable gas) enters the bubble columnhumidification region. The humidification region gas inlet stream mayflow through the bubble generator of the at least one stage of thehumidification region, thereby forming a plurality of gas bubbles. Insome cases, the gas bubbles flow through the liquid layer of the atleast one stage of the humidification region. As the gas bubblesdirectly contact the liquid layer, which may have a higher temperaturethan the gas bubbles, heat and/or mass (e.g., the condensable fluid) maybe transferred from the liquid layer to the gas bubbles through anevaporation (e.g., humidification) process, thereby forming a heated, atleast partially humidified humidification region gas outlet stream and ahumidification region liquid outlet stream having a higher concentrationof the one or more contaminants than the humidification region liquidinlet stream. In certain embodiments, the condensable fluid is water,and the vapor-containing humidification region gas outlet stream isenriched in water vapor relative to the humidification region gas inletstream received from the humidification region gas inlet. In someembodiments, bubbles of the heated, at least partially humidified gasexit the liquid layer and recombine in the vapor distribution region,and the heated, at least partially humidified gas is substantiallyevenly distributed throughout the vapor distribution region. Thehumidification region gas outlet stream and humidification region liquidoutlet stream may then exit the humidification region.

In some cases, the bubble column dehumidification region is configuredto receive the humidification region gas outlet stream (e.g., comprisingthe heated, at least partially humidified gas) as a dehumidificationregion gas inlet stream. The dehumidification region gas inlet streammay flow through the bubble generator of the at least one stage of thedehumidification region, thereby forming a plurality of bubbles of theheated, at least partially humidified gas. In some cases, the gasbubbles flow through the liquid layer of the at least one stage of thedehumidification region. As the gas bubbles directly contact the liquidlayer, which may have a lower temperature than the gas bubbles, heatand/or mass (e.g., condensable fluid) may be transferred from the gasbubbles to the liquid layer via a condensation (e.g., dehumidification)process, thereby forming a cooled, at least partially dehumidifieddehumidification region gas outlet stream and a dehumidification regionliquid outlet stream comprising the condensable fluid in liquid phase.In certain embodiments, the condensable fluid is water, and thedehumidification region gas outlet stream is lean in water vaporrelative to the dehumidification region gas inlet stream received fromthe dehumidification region gas inlet. In some embodiments, bubbles ofthe cooled, at least partially dehumidified gas exit the liquid layerand recombine in the vapor distribution region, and the cooled, at leastpartially dehumidified gas is substantially evenly distributedthroughout the vapor distribution region. The dehumidification regiongas outlet stream and dehumidification region liquid outlet stream maythen exit the dehumidification region.

FIG. 1A shows, according to some embodiments, a schematiccross-sectional diagram of an exemplary combined bubble column apparatus100 comprising a vessel 150 comprising a bubble column humidificationregion 102 and a bubble column dehumidification region 104. As shown inFIG. 1A, humidification region 102 comprises a single stage comprising ahumidification region liquid inlet 106, a humidification region liquidoutlet 108, and a humidification chamber 110. Liquid layer 112 occupiesa portion of humidification chamber 110. In some embodiments, liquidlayer 112 comprises a condensable fluid in liquid phase (e.g., liquidwater) and one or more contaminants (e.g., dissolved salts). In someembodiments, a vapor distribution region 114 occupies at least a portionof humidification chamber 110 that is not occupied by liquid layer 112.Humidification chamber 110 may, in addition, comprise weir 116, whichmay limit the height of liquid layer 112. Humidification chamber 110 mayalso comprise bubble generator 118, which may be in fluid communicationwith humidification chamber 110 and/or may be arranged withinhumidification chamber 110. In some cases, bubble generator 118 formsthe bottom surface of humidification chamber 110 and/or acts as a gasinlet for humidification chamber 110. In some embodiments, vessel 150 ofapparatus 100 further comprises gas distribution chamber 136 positionedbelow humidification region 102. In FIG. 1A, gas distribution chamber136 is in fluid communication with apparatus gas inlet 138 and withhumidification chamber 110 via bubble generator 118. Bubble generator118 may form a bottom surface of humidification chamber 110 and a topsurface of gas distribution chamber 136. Gas distribution chamber 136may comprise gas distribution region 140, which represents the spacewithin chamber 136 throughout which a gas entering through apparatus gasinlet 138 is distributed.

As shown in FIG. 1A, dehumidification region 104 is positioned abovehumidification region 102. Dehumidification region 104 comprisesdehumidification region liquid inlet 120, dehumidification region liquidoutlet 122, apparatus gas outlet 124, and dehumidification chamber 126.Liquid layer 128 may occupy at least a portion of dehumidificationchamber 126. In some embodiments, liquid layer 128 comprises thecondensable fluid in liquid phase (e.g., liquid water). In someembodiments, a vapor distribution region 130 occupies at least a portionof dehumidification chamber 126 that is not occupied by liquid layer128. In addition, dehumidification chamber 126 may comprise weir 132,which may limit the height of liquid layer 128. In some cases,dehumidification chamber 126 comprises bubble generator 134, which maybe in fluid communication with dehumidification chamber 126 and/or maybe arranged within dehumidification chamber 126. In some cases, bubblegenerator 134 forms the bottom surface of dehumidification chamber 126and/or acts as a gas inlet for dehumidification chamber 126. As shown inFIG. 1A, bubble generator 134 forms a bottom surface of dehumidificationchamber 126 and a top surface of humidification chamber 110.

In operation, a liquid stream comprising the condensable fluid in liquidphase and one or more contaminants may enter humidification region 102through humidification region liquid inlet 106, flowing into liquidlayer 112 in humidification chamber 110. The liquid stream may flowacross humidification chamber 110 to weir 116 and exit humidificationchamber 110 through humidification region liquid outlet 108. Weir 116may maintain the height of liquid layer 112 at the height of weir 116(e.g., excess liquid may flow over weir 116 to humidification regionliquid outlet 108). In dehumidification region 104, a liquid streamcomprising the condensable fluid in liquid phase may enter throughdehumidification region liquid inlet 120, flowing into liquid layer 128in dehumidification chamber 126. The liquid stream may flow acrossdehumidification chamber 126 to weir 132 and exit dehumidificationchamber 126 through dehumidification region liquid outlet 122.

In some cases, apparatus gas inlet 138 is in fluid communication with asource of a gas (e.g., a non-condensable gas). The gas may enter vessel150 of apparatus 100 through apparatus gas inlet 138, flowing into gasdistribution chamber 136. After being substantially homogeneouslydistributed throughout gas distribution region 140 of gas distributionchamber 136, the gas may pass through bubble generator 118, producing aplurality of gas bubbles that travel through liquid layer 112 inhumidification chamber 110. The temperature of liquid layer 112 may behigher than the temperature of the gas bubbles, resulting in transfer ofheat and/or mass from liquid layer 112 to the gas bubbles through ahumidification process. In certain cases, the transfer of heat and/ormass may increase the temperature of the gas, and thus the amount of thecondensable fluid that it can carry. After passing through liquid layer112, the gas, which has been heated and at least partially humidified,may enter vapor distribution region 114 within humidification chamber110. In some cases, the gas may be substantially evenly distributedthroughout vapor distribution region 114. The heated, at least partiallyhumidified gas may then pass through bubble generator 134, therebyforming a plurality of bubbles of the heated, at least partiallyhumidified gas. The bubbles of the heated, at least partially humidifiedgas may then travel through liquid layer 128 in dehumidification chamber126. The liquid (e.g., condensable fluid in liquid phase) of liquidlayer 128 may have a lower temperature than the bubbles of the heated,at least partially humidified gas. As the gas bubbles travel throughliquid layer 128, heat and/or mass may be transferred from the gasbubbles to liquid layer 128 through a dehumidification process. Aftertraveling through liquid layer 128, bubbles of the cooled, at leastpartially dehumidified gas may enter vapor distribution region 130within dehumidification chamber 126. The cooled, at least partiallydehumidified gas may then exit vessel 150 of apparatus 100 via apparatusgas outlet 124.

Appropriate conditions under which to operate the combined HDHapparatuses (e.g., combined bubble column apparatuses) described hereinfor desired performance may be selected by an operator of the systemand/or by an algorithm. In some embodiments, the pressure in the vesselof the combined HDH apparatus may be selected to be approximatelyambient atmospheric pressure during operation. According to certainembodiments, the pressure in the vessel of the combined HDH apparatusmay be selected to be about 90 kPa or less during operation. It may bedesirable, in some embodiments, for the pressure in the humidificationregion of the vessel to be less than approximately ambient atmosphericpressure during operation. In some cases, as the pressure inside thehumidification region decreases, the ability of the humidified carriergas to carry more water vapor increases, allowing for increasedproduction of substantially pure water when the carrier gas isdehumidified in the dehumidification region. Without wishing to be boundby a particular theory, this effect may be explained by the humidityratio, which generally refers to the ratio of water vapor mass to dryair mass in moist air, being higher at pressures lower than atmosphericpressure.

In some embodiments, the combined HDH apparatus (e.g., combined bubblecolumn apparatus) may have a relatively low pressure drop duringoperation. As used herein, the pressure drop across an apparatus refersto the difference between the pressure of a gas stream entering theapparatus at an inlet and the pressure of a gas stream exiting theapparatus at an outlet. In FIG. 1A, for example, the pressure dropacross apparatus 100 would be the difference between the pressure of thegas at apparatus gas inlet 138 and the pressure of the gas at apparatusgas outlet 124. In some cases, the pressure drop may not include theeffect of pressure-increasing devices (e.g., fans, blowers, compressors,pumps). For example, in certain cases, the pressure drop may be obtainedby subtracting the effect of one or more pressure-increasing devices ona gas stream from the difference between the pressure of the gas streamentering the apparatus at an inlet and the pressure of the gas streamexiting the apparatus at an outlet. In some embodiments, the pressuredrop across the apparatus is about 200 kPa or less, about 150 kPa orless, about 100 kPa or less, about 75 kPa or less, about 50 kPa or less,about 20 kPa or less, about 15 kPa or less, about 10 kPa or less, about5 kPa or less, about 2 kPa or less, or about 1 kPa or less. In certainembodiments, the pressure drop across the apparatus (e.g., difference inpressure between the outlet and the inlet) is in the range of about 1kPa to about 2 kPa, about 1 kPa to about 5 kPa, about 1 kPa to about 10kPa, about 1 kPa to about 15 kPa, about 1 kPa to about 20 kPa, about 1kPa to about 50 kPa, about 1 kPa to about 75 kPa, about 1 kPa to about100 kPa, about 1 kPa to about 150 kPa, or about 1 kPa to about 200 kPa.In some embodiments, the pressure of the gas at inlet 138 issubstantially the same as the pressure of the gas at outlet 124 (e.g.,the pressure drop is substantially zero).

In some cases, inlets and/or outlets within the humidification regionand/or the dehumidification region may be provided as separate anddistinct structural elements/features. In some cases, inlets and/oroutlets within the humidification region and/or the dehumidificationregion may be provided by certain components such as the bubblegenerator and/or any other features that establish fluid communicationbetween components of the apparatus. For example, the “gas inlet” and/or“gas outlet” of a humidification region or a dehumidification region maybe provided as a plurality of holes of a bubble generator (e.g., asparger plate). In some embodiments, at least one bubble generator iscoupled to a gas inlet of a stage of the humidification region and/orthe dehumidification region. In some embodiments, a bubble generator iscoupled to a gas inlet of each stage of the humidification region and/ordehumidification region.

The bubble generators may have various features (e.g., holes) used forgeneration of bubbles. The selection of a bubble generator can affectthe size and/or shape of the gas bubbles generated, thereby affectingheat and/or mass transfer between gas bubbles and a liquid layer of ahumidification region or a dehumidification region. Appropriate bubblegenerator and/or bubble generator conditions (e.g., bubble generatorspeeds) may be selected to produce a particular desired set of gasbubbles. Non-limiting examples of suitable bubble generators include asparger plate (e.g., a plate comprising a plurality of holes throughwhich a gas can travel), a device comprising one or more perforatedpipes (e.g., having a radial, annular, spider-web, or hub-and-spokeconfiguration), a device comprising one or more nozzles, and/or porousmedia (e.g., microporous metal).

In some embodiments, a bubble generator comprises a sparger plate. Ithas been recognized that a sparger plate may have certain advantageouscharacteristics. For example, the pressure drop across a sparger platemay be relatively low. Additionally, the simplicity of the sparger platemay render it inexpensive to manufacture and/or resistant to the effectsof fouling. According to some embodiments, the sparger plate comprises aplurality of holes, at least a portion of which have a diameter (ormaximum cross-sectional dimension for non-circular holes) in the rangeof about 0.1 mm to about 50 mm, about 0.1 mm to about 25 mm, about 0.1mm to about 15 mm, about 0.1 mm to about 10 mm, about 0.1 mm to about 5mm, about 0.1 mm to about 1 mm, about 1 mm to about 50 mm, about 1 mm toabout 25 mm, about 1 mm to about 15 mm, about 1 mm to about 10 mm, orabout 1 mm to about 5 mm. In certain embodiments, substantially all theholes of the plurality of holes have a diameter (or maximumcross-sectional dimension) in the range of about 0.1 mm to about 50 mm,about 0.1 mm to about 25 mm, about 0.1 mm to about 15 mm, about 0.1 mmto about 10 mm, about 0.1 mm to about 5 mm, about 0.1 mm to about 1 mm,about 1 mm to about 50 mm, about 1 mm to about 25 mm, about 1 mm toabout 15 mm, about 1 mm to about 10 mm, or about 1 mm to about 5 mm. Theholes may have any suitable shape. For example, at least a portion ofthe plurality of holes may be substantially circular, substantiallyelliptical, substantially square, substantially rectangular,substantially triangular, and/or irregularly shaped. In someembodiments, substantially all the holes of the plurality of holes aresubstantially circular, substantially elliptical, substantially square,substantially rectangular, substantially triangular, and/or irregularlyshaped.

In some cases, the sparger plate may be arranged along the bottomsurface of a stage within the humidification region and/or thedehumidification region. In some embodiments, the sparger plate may havea surface area that covers at least about 50%, at least about 60%, atleast about 70%, at least about 80%, at least about 90%, at least about95%, or about 100% of a cross-section of the humidification regionand/or the dehumidification region.

In some embodiments, a combined HDH apparatus (e.g., a combined bubblecolumn apparatus) further comprises an optional stack. A stack generallyrefers to a structure (e.g., conduit) in fluid communication with a gasoutlet of the combined HDH apparatus, where the maximum cross-sectionaldimension (e.g., diameter) and/or length of the stack is larger than thecorresponding maximum cross-sectional dimension and/or length of the gasoutlet. In some cases, a stack may reduce or eliminate dropletentrainment (e.g., droplets of liquid flowing out of the apparatus withthe gas stream). Without wishing to be bound by a particular theory,increasing the maximum cross-sectional dimension of a conduit throughwhich a gas stream flows will tend to reduce the velocity of the gasstream. As a result, dimensions of the stack may be determined orselected for a given gas stream flow volume that can result in a gasstream velocity in the stack that may be insufficient to entrain anyliquid droplets or at least some liquid droplets that may be present inthe gas stream, the result being that such droplets may fall out of thegas stream instead of exiting the apparatus. For example, in certaincases, the drag force on a liquid droplet (assuming such droplet issubstantially spherical in shape) in a gas stream may be approximated byStokes' Law:

F _(drag)=6πμRV

where F_(drag) is the drag force exerted on the droplet (e.g., by themoving gas stream), μ is the dynamic viscosity of the gas, R is theradius of the droplet, and V is the velocity of the gas relative to thevelocity of the droplet. In some cases, when F_(drag) is greater thanthe gravitational force acting on the droplet, the droplet may remainentrained and may exit the apparatus with the gas stream. In some cases,when F_(drag) is less than the gravitational force acting on thedroplet, the droplet may fall out of the gas stream and return to theapparatus. According to some embodiments, the expanded maximumcross-sectional dimension of the stack (e.g., compared to the maximumcross-sectional dimension of the gas outlet) may cause the velocity ofthe gas stream flowing through the stack (e.g., the dehumidified gasstream) to be reduced. According to Stokes' Law, reducing the velocityof the gas stream flowing through the stack may reduce the drag forceexerted on liquid droplets in the gas stream. In certain cases, the dragforce may be reduced to such an extent that the drag force exerted onthe droplets becomes less than the gravitational force. Accordingly, incertain embodiments, as a gas stream containing entrained liquiddroplets flows into a stack having an expanded cross-sectional dimensionrelative to the gas outlet, one or more of the entrained liquid dropletsmay fall out of the gas stream and return to a liquid layer of theapparatus (e.g., through the gas outlet and/or a separate conduit). In aparticular, non-limiting embodiment, one or more entrained liquiddroplets may fall out of a gas stream flowing through the stack and mayform a surface film on the sides of the stack. In the particularembodiment, liquid droplets may subsequently flow from the surface filmon the sides of the stack to a liquid layer of the apparatus.

FIG. 1B shows, according to some embodiments, a schematic illustrationof an exemplary apparatus 100 comprising optional stack 142 in fluidcommunication with apparatus gas outlet 124. In some cases, stack 142may prevent droplets of liquid from liquid layer 128 from flowing out ofapparatus 100 with a dehumidification region gas outlet stream (e.g., adehumidified gas stream). Instead, liquid droplets present in thedehumidified gas stream may fall out of the dehumidified gas stream andreturn to liquid layer 128 (e.g., through gas outlet 124 and/or aseparate conduit). As shown in FIG. 1B, in some cases, stack 142 has amaximum cross-sectional dimension (e.g., length, diameter) D_(s) that isgreater than the maximum cross-sectional dimension D_(o) of gas outlet124. In certain embodiments, the maximum cross-sectional dimension D_(s)of the stack is at least about 0.01 m, at least about 0.02 m, at leastabout 0.05 m, at least about 0.1 m, at least about 0.2 m, at least about0.5 m, at least about 1 m, at least about 2 m, or at least about 5 mgreater than the maximum cross-sectional dimension D_(o) of the outlet.In some embodiments, maximum cross-sectional dimension D_(s) of thestack is greater than maximum cross-sectional dimension D_(o) of theoutlet by an amount in the range of about 0.01 m to about 0.05 m, about0.01 m to about 0.1 m, about 0.01 m to about 0.5 m, about 0.01 m toabout 1 m, about 0.01 m to about 5 m, about 0.1 m to about 0.5 m, about0.1 m to about 1 m, about 0.1 m to about 5 m, about 0.5 m to about 1 m,about 0.5 m to about 5 m, or about 1 m to about 5 m.

In some embodiments, a combined HDH apparatus (e.g., a combined bubblecolumn apparatus) optionally comprises one or more droplet eliminators.A droplet eliminator generally refers to a device or structureconfigured to prevent entrainment of liquid droplets. Non-limitingexamples of suitable types of droplet eliminators include mesheliminators (e.g., wire mesh mist eliminators), vane eliminators (e.g.,vertical flow chevron vane mist eliminators, horizontal flow chevronvane mist eliminators), cyclonic separators, vortex separators, dropletcoalescers, and/or knockout drums. In some cases, the droplet eliminatormay be configured such that liquid droplets entrained in a gas streamcollide with a portion of the droplet eliminator and fall out of the gasstream. In certain embodiments, the droplet eliminator may extend acrossthe opening (e.g., mouth) of one or more gas outlets.

In some cases, a droplet eliminator may be positioned within a combinedHDH apparatus (e.g., a combined bubble column apparatus) upstream of agas outlet of a humidification region and/or a dehumidification region.For example, in FIG. 1B, combined bubble column apparatus 100 comprisesa first droplet eliminator 144 positioned between humidification chamber110 and dehumidification chamber 126 (e.g., upstream of bubble generator134, which acts as a gas outlet of humidification region 102). Inaddition, combined bubble column apparatus 100 comprises a seconddroplet eliminator 148 positioned between dehumidification chamber 126and apparatus gas outlet 124, which acts as a gas outlet ofdehumidification region 104. In operation, liquid droplets in a gasstream flowing through apparatus 100 may encounter first dropleteliminator 144 and/or second droplet eliminator 148 and return to aliquid layer (e.g., liquid layer 112 and/or liquid layer 128).

In some cases, reducing or eliminating droplet entrainment mayadvantageously increase the amount of condensable fluid in liquid phase(e.g., purified water) recovered from a combined HDH apparatus (e.g., byreducing the amount of condensable fluid lost through an apparatus gasoutlet). In certain embodiments, reducing or eliminating dropletentrainment may increase the amount of condensable fluid in liquid phase(e.g., purified water) recovered from a combined HDH apparatus by atleast about 1%, at least about 5%, at least about 10%, at least about15%, at least about 20%, at least about 30%, at least about 40%, atleast about 50%, or at least about 60%. In some cases, reducing oreliminating droplet entrainment may increase the amount of condensablefluid recovered from a combined HDH apparatus by an amount in the rangeof about 1% to about 10%, about 1% to about 20%, about 1% to about 40%,about 1% to about 60%, about 5% to about 20%, about 5% to about 40%,about 5% to about 60%, about 10% to about 20%, about 10% to about 30%,about 10% to about 40%, about 10% to about 50%, about 10% to about 60%,about 20% to about 30%, about 20% to about 40%, about 20% to about 50%,about 20% to about 60%, about 30% to about 40%, about 30% to about 50%,about 30% to about 60%, about 40% to about 50%, about 40% to about 60%,or about 50% to about 60%.

In some embodiments, a combined HDH apparatus (e.g., a combined bubblecolumn apparatus) optionally comprises a liquid collector. A liquidcollector generally refers to a structure or device configured tocollect a liquid while allowing a gas to freely flow through it.Examples of suitable types of liquid collectors include, but are notlimited to, deck collectors, trough collectors, and vane collectors.According to some embodiments, a liquid collector is configured tocollect water that falls on it from above (e.g., from a dehumidificationregion positioned above the liquid collector) while allowing a gasstream (e.g., a humidification region gas outlet stream comprising aheated, at least partially humidified gas) to freely flow through theliquid collector. In some cases, the liquid collector advantageouslyprevents liquid from a dehumidification region of a combined HDHapparatus from flowing to a humidification region of the combined HDHapparatus. For example, if gas flow through a combined bubble columnapparatus is terminated while liquid remains in one or more stages ofthe dehumidification region, the liquid may exit the one or more stagesthrough one or more bubble generators (e.g., through the holes ofsparger plates). The presence of a liquid collector may, in some cases,prevent the liquid exiting the one or more dehumidification stages fromentering the humidification region. This may avoid, for example, thecommingling of liquid from the dehumidification region, which maycomprise a condensable fluid in liquid phase (e.g., substantially purewater), with liquid from the humidification region, which may comprisethe condensable fluid in liquid phase and one or more contaminants(e.g., salt-containing water). In certain embodiments, the liquidcollector may act as a liquid sump volume for the dehumidificationregion.

In some cases, a liquid collector is positioned between thehumidification region and the dehumidification region of a combined HDHapparatus (e.g., a combined bubble column apparatus). In someembodiments, the liquid collector is positioned between a vapordistribution region of a stage of the humidification region (e.g., thelast stage of the humidification region through which a gas streamflows) and a bubble generator of a stage of the dehumidification region(e.g., the first stage of the dehumidification region through which agas stream flows). In certain embodiments, the liquid collector ispositioned between a droplet eliminator and a bubble generator of astage of the dehumidification region (e.g., the first stage of thedehumidification region through which a gas stream flows). For example,in FIG. 1B, liquid collector 146 is positioned between dropleteliminator 144 and bubble generator 134 of dehumidification chamber 126.

In some embodiments, the humidification region and/or dehumidificationregion of a vessel of a combined HDH apparatus (e.g., a combined bubblecolumn apparatus) comprise a plurality of stages. In some cases, thestages may be arranged such that a gas flows sequentially from a firststage to a second stage. In some cases, the stages may be verticallyarranged (e.g., a second stage may be positioned above or below a firststage in an apparatus) or horizontally arranged (e.g., a second stagemay be positioned to the right or left of a first stage in anapparatus). The stages may be arranged such that a gas stream flowssequentially through a first stage, a second stage, a third stage, andso on. In some cases, each stage may comprise a liquid layer. Inembodiments relating to humidification regions comprising a plurality ofstages (e.g., multi-stage humidification regions), the temperature of aliquid layer of a first stage (e.g., the bottommost stage in avertically arranged humidification region) may be lower than thetemperature of a liquid layer of a second stage (e.g., a stagepositioned above the first stage in a vertically arranged humidificationregion), which may be lower than the temperature of a liquid layer of athird stage (e.g., a stage positioned above the second stage in avertically arranged humidification region). In some embodiments, eachstage in a multi-stage humidification region operates at a temperatureabove that of the previous stage (e.g., the stage below it, inembodiments comprising vertically arranged humidification regions). Inembodiments relating to dehumidification regions comprising a pluralityof stages (e.g., multi-stage dehumidification regions), the temperatureof a liquid layer of a first stage (e.g., the bottommost stage in avertically arranged dehumidification region) may be higher than thetemperature of a liquid layer of a second stage (e.g., a stagepositioned above the first stage in a vertically arrangeddehumidification region), which may be higher than the temperature of aliquid layer of a third stage (e.g., a stage positioned above the secondstage in a vertically arranged dehumidification region). In someembodiments, each stage in a multi-stage dehumidification regionoperates at a temperature below that of the previous stage (e.g., thestage below it, in embodiments comprising vertically arrangeddehumidification regions).

The presence of multiple stages within the humidification region and/ordehumidification region of a combined HDH apparatus may, in some cases,advantageously result in increased humidification and/ordehumidification of a gas. In some cases, the presence of multiplestages may advantageously lead to higher recovery of a condensable fluidin liquid phase. For example, the presence of multiple stages mayprovide numerous locations where the gas may be humidified and/ordehumidified (e.g., treated to recover the condensable fluid). That is,the gas may travel through more than one liquid layer in which at leasta portion of the gas undergoes humidification (e.g., evaporation) ordehumidification (e.g., condensation). In addition, the presence ofmultiple stages may increase the difference in temperature between aliquid stream at an inlet and an outlet of a humidification regionand/or dehumidification region. For example, the use of multiple stagescan produce a dehumidification region liquid outlet stream havingincreased temperature relative to the dehumidification region liquidinlet stream, as discussed more fully below. This may be advantageous insystems where heat from a liquid stream (e.g., dehumidification regionliquid outlet stream) is transferred to a separate stream (e.g.,humidification region liquid inlet stream) within the system. In suchcases, the ability to produce a heated dehumidification region liquidoutlet stream can increase the energy effectiveness of the system.Additionally, the presence of multiple stages may enable greaterflexibility for fluid flow within an apparatus. For example, asdiscussed in further detail below, extraction and/or injection of fluids(e.g., gas streams) from intermediate humidification and/ordehumidification stages may occur through intermediate exchangeconduits.

It should be understood that the humidification region and/ordehumidification region of a vessel of a combined HDH apparatus may haveany number of stages. In some embodiments, the humidification regionand/or dehumidification region may have at least one, at least two, atleast three, at least four, at least five, at least six, at least seven,at least eight, at least nine, or at least ten or more stages. In someembodiments, the humidification region and/or dehumidification regionmay have no more than one, no more than two, no more than three, no morethan four, no more than five, no more than six, no more than seven, nomore than eight, no more than nine, or no more than ten stages. In someembodiments, the stages may be arranged such that they are substantiallyparallel to each other. In certain cases, the stages may be positionedat an angle.

In some cases, at least one stage of the plurality of stages of ahumidification region and/or dehumidification region of a vessel of acombined HDH apparatus comprises a chamber in fluid communication withone or more bubble generators. In some cases, a liquid layer occupies aportion of the chamber. In some embodiments, a vapor distribution regioncomprises at least a portion of the chamber not occupied by the liquidlayer (e.g., the portion of the chamber above the liquid layer). In someembodiments, the vapor distribution region is positioned between twoliquid layers of two consecutive stages. The vapor distribution regionmay, in certain cases, advantageously damp out flow variations createdby random bubbling by allowing a gas to redistribute evenly across thecross section of the vessel of the apparatus. Additionally, in the freespace of the vapor distribution region, large droplets entrained in thegas may have some space to fall back into the liquid layer before thegas enters the subsequent stage. The vapor distribution region may alsoserve to separate two subsequent stages, thereby increasing thethermodynamic effectiveness of the apparatus by keeping the liquidlayers of each stage separate. As discussed in further detail below, thechamber may further comprise one or more weirs and/or baffles to controlliquid flow through the chamber. The chamber may, additionally, compriseone or more conduits (e.g., liquid conduits) to adjacent stages.

FIG. 2A shows a schematic cross-sectional diagram of an exemplarymulti-stage combined bubble column apparatus, according to someembodiments. In FIG. 2A, combined bubble column apparatus 200 comprisesvessel 294 comprising gas distribution chamber 202, humidificationregion 204, and dehumidification region 206. Humidification region 204may be arranged vertically above gas distribution chamber 202, anddehumidification region 206 may be arranged vertically abovehumidification region 204. In some embodiments, gas distribution chamber202 comprises an apparatus gas inlet 208 and a humidification regionliquid outlet 210. Apparatus gas inlet 208 may be fluidly connected to asource of a first gas comprising a condensable fluid in vapor phaseand/or a non-condensable gas (not shown in FIG. 2A). In some cases, gasdistribution chamber 202 comprises a gas distribution region 212,throughout which a gas entering through apparatus gas inlet 208 issubstantially evenly distributed (e.g., along a bottom surface of bubblegenerator 226). In some embodiments, gas distribution chamber 202further comprises liquid sump volume 214 occupying at least a portion ofgas distribution chamber 202 that is not occupied by gas distributionregion 212. In some cases, liquid collects in sump volume 214 afterexiting humidification region 204 prior to exiting vessel 294 ofapparatus 200. As shown in FIG. 2A, sump volume 214 may be in directcontact with humidification region liquid outlet 210. Sump volume 214and humidification region liquid outlet 210 may, in some cases, be influid communication with a pump that pumps liquid out of vessel 294 ofcombined bubble column apparatus 200 (not shown in FIG. 2A). In somecases, sump volume 214 may provide a positive suction pressure on theintake of the pump and may advantageously prevent negative suctionpressure that may induce cavitation bubbles. Sump volume 214 may alsodecrease the sensitivity of apparatus 200 to sudden changes in heattransfer rates.

As shown in FIG. 2A, humidification region 204 comprises firsthumidification stage 216 and second humidification stage 218, wheresecond humidification stage 218 is arranged vertically above firsthumidification stage 216. First humidification stage 216 compriseschamber 220, which is partially occupied by liquid layer 222. In somecases, liquid layer 222 comprises a condensable fluid in liquid phaseand one or more contaminants (e.g., dissolved salts). A vapordistribution region 224 may occupy at least a portion of humidificationchamber 220 that is not occupied by liquid layer 222 (e.g., the regionabove liquid layer 222). Vapor distribution region 224 may be positionedbetween liquid layer 222 of first humidification stage 216 and liquidlayer 238 of second humidification stage 218. In FIG. 2A, humidificationchamber 220 is in fluid communication with bubble generator 226, whichmay act as a gas inlet of first humidification stage 216 and allow fluidcommunication between gas distribution chamber 202 and firsthumidification stage 216, and bubble generator 244, which may act as agas outlet of first humidification stage 216 and allow fluidcommunication between first humidification stage 216 and secondhumidification stage 218. Bubble generator 226 may occupy substantiallythe entire bottom surface of first humidification stage 216 or mayoccupy a smaller portion of the bottom surface of first humidificationstage 216. Bubble generator 244 may occupy substantially the entire topsurface of first humidification stage 216 or may occupy a smallerportion of the top surface of first humidification stage 216.Humidification chamber 220 may also be in fluid communication withdowncomer 228, which provides a liquid conduit between first stage 216and second stage 218, and downcomer 230, which provides a liquid conduitbetween first stage 216 and gas distribution chamber 202. Downcomer 228,which is positioned between first stage 216 and second stage 218,provides a path for any overflowing condensable fluid (e.g., from liquidlayer 238) to travel from second stage 218 to first stage 216.

Chamber 220 may also comprise one or more liquid flow structures (e.g.,weirs and/or baffles). For example, as shown in FIG. 2A, chamber 220comprises first weir 232 and second weir 234. First weir 232 ispositioned downstream of downcomer 228 and may form a pool surroundingthe outlet of downcomer 228. The outlet of downcomer 228 may besubmerged in the pool, thereby preventing the gas flowing through firststage 216 from flowing to second stage 218 through downcomer 228 insteadof through bubble generator 244. For example, in some cases, the pool ofliquid surrounding the outlet of downcomer 228 has a height higher thanthe height of liquid layer 222 (e.g., the height of weir 232 is higherthan the height of liquid layer 222). This may advantageously result inan increased hydrostatic head around downcomer 228, such that gasbubbles preferentially flow through liquid layer 222 instead of throughthe pool of liquid surrounding downcomer 228 (e.g., the hydrostatic headof liquid that the gas has to overcome is higher in the pool of liquidsurrounding downcomer 228 than in liquid layer 222), preventing the gasfrom bypassing bubble generator 244. In some cases, allowing the gas toflow through downcomer 228 to bypass bubble generator 244 may have thedeleterious effect of disrupting the flow of liquid through apparatus200 and may, in certain cases, stop operation of apparatus 200 entirely.In certain embodiments, the pool of liquid surrounding downcomer 228 hasa height higher than the height of liquid layer 222 and higher than theheight of liquid layer 238. In certain cases, the portion of the bottomsurface of chamber 220 around and/or beneath downcomer 228 (e.g., theportion of the bottom surface of chamber 220 between weir 232 and an endwall) is substantially impermeable to gas flow (e.g., does not comprisea bubble generator), and any pool of liquid surrounding downcomer 228may have a height that is higher than, lower than, or equal to theheight of liquid layer 222 and/or liquid layer 238. In some embodiments,the distance D (e.g., vertical distance) between the top of weir 232 andthe bottom of the outlet of downcomer 228 (indicated as 296 in FIG. 2A)is greater than the height of liquid layer 238. This may, in some cases,advantageously prevent back flow through downcomer 228. In certainembodiments, the distance D (e.g., vertical distance) between the top ofweir 232 and the bottom of the outlet of downcomer 228 is greater thanthe height of liquid layer 222 and greater than the height of liquidlayer 238. In some cases, second weir 234 is positioned upstream ofdowncomer 230 and establishes the maximum height of liquid layer 222,such that any liquid above that height would flow over weir 234, throughdowncomer 230, to liquid sump volume 214. Weir 232 and weir 234 may bepositioned such that liquid entering first humidification stage 216 isdirected to flow from first weir 232 to second weir 234.

Second humidification stage 218 comprises humidification chamber 236 andliquid layer 238 positioned within chamber 236. Liquid layer 238 is influid communication with humidification region liquid inlet 240, whichmay be fluidly connected to a source of a liquid comprising acondensable fluid in liquid phase and one or more contaminants (e.g.,dissolved salts). In some embodiments, a vapor distribution region 242occupies at least a portion of humidification chamber 236 that is notoccupied by liquid layer 238 (e.g., the region above liquid layer 238).In FIG. 2A, humidification chamber 236 is in fluid communication withbubble generator 244, which may act as a gas inlet of secondhumidification stage 218 and allow fluid communication between firsthumidification stage 216 and second humidification stage 218, and bubblegenerator 246, which may act as a gas outlet of second humidificationstage 218 and allow fluid communication between second humidificationstage 218 and first dehumidification stage 250. Bubble generator 244 mayoccupy substantially the entire bottom surface of second humidificationstage 218 or may occupy a smaller portion of the bottom surface ofsecond humidification stage 218. Bubble generator 246 may occupysubstantially the entire top surface of second humidification stage 218or may occupy a smaller portion of the top surface of secondhumidification stage 218. Humidification chamber 236 may also be influid communication with downcomer 228. Humidification chamber 236 mayfurther comprise weir 248, which may be positioned upstream of downcomer228. Weir 248 may establish the maximum height of liquid layer 238, suchthat any liquid that would exceed the height of weir 248 would flow overweir 248, through downcomer 228, and into liquid layer 222 of firsthumidification stage 216. Weir 248 may be positioned such that liquidmay flow across humidification chamber 236 from humidification regionliquid inlet 240 to weir 248.

As shown in FIG. 2A, dehumidification region 206 comprises firstdehumidification stage 250 and second dehumidification stage 252, wheresecond dehumidification stage 252 is arranged vertically above firstdehumidification stage 250. First dehumidification stage 250 comprisesdehumidification chamber 254, which is partially occupied by liquidlayer 256. In some cases, liquid layer 256, which may be in fluidcommunication with dehumidification region liquid outlet 258, comprisesthe condensable fluid in liquid phase (e.g., substantially pure water).A vapor distribution region 260 may occupy at least a portion of chamber254 that is not occupied by liquid layer 256 (e.g., the region aboveliquid layer 256). Vapor distribution region 260 may be positionedbetween liquid layer 256 of first dehumidification stage 250 and liquidlayer 276 of second dehumidification stage 252. In FIG. 2A,dehumidification chamber 254 is in fluid communication with bubblegenerator 246, which may act as a gas inlet of first dehumidificationstage 250 and facilitate fluid communication between secondhumidification stage 218 and first dehumidification stage 250, andbubble generator 262, which may act as a gas outlet of firstdehumidification stage 250 and facilitate fluid communication betweenfirst dehumidification stage 250 and second dehumidification stage 252.Bubble generator 246 may occupy substantially the entire bottom surfaceof first dehumidification stage 250 or may occupy a smaller portion ofthe bottom surface of first dehumidification stage 250. Bubble generator262 may occupy substantially the entire top surface of firstdehumidification stage 250 or may occupy a smaller portion of the topsurface of first dehumidification stage 250.

In FIG. 2A, dehumidification chamber 254 of first dehumidification stage250 is also in fluid communication with downcomer 264, which provides aliquid conduit between first stage 250 and second stage 252 ofdehumidification region 206. Dehumidification chamber 254 may alsocomprise first weir 266 and second weir 268. First weir 266 may belocated downstream of downcomer 264 and may establish a pool of liquidaround the outlet of downcomer 264 having a height higher than theheight of liquid layer 256 (e.g., the height of weir 266 may be higherthan the height of liquid layer 256). First weir 266 may be configuredto prevent a gas stream flowing through first dehumidification stage 250from bypassing bubble generator 262. In some embodiments, the distance(e.g., vertical distance) between the top of first weir 266 and thebottom of the outlet of downcomer 264 is greater than the height ofliquid layer 276. In some embodiments, second weir 268 may be positionedupstream of dehumidification region liquid outlet 258. Second weir 268may establish the maximum height of liquid layer 256 (e.g., any liquidthat would cause the height of liquid layer 256 to exceed the height ofweir 268 would flow over weir 268 and exit through outlet 258). In somecases, dehumidification stage 250 may be configured such that liquidentering first dehumidification stage 250 via downcomer 264 flows fromfirst weir 266 to second weir 268.

Second dehumidification stage 252 comprises dehumidification chamber270, which may be in fluid communication with bubble generator 262,dehumidification region liquid inlet 272, apparatus gas outlet 274, anddowncomer 264. Bubble generator 262 may act as a gas inlet to seconddehumidification stage 252 and may allow fluid communication betweenfirst dehumidification stage 250 and second dehumidification stage 252.For example, bubble generator 262 may be arranged to receive the gasfrom first dehumidification stage 250. Bubble generator 262 may occupysubstantially the entire bottom surface of second stage 252 or mayoccupy a smaller portion of the bottom surface of second stage 252.Downcomer 264 may provide a liquid conduit between first stage 250 andsecond stage 252 of dehumidification region 206. Chamber 270 may be atleast partially occupied by liquid layer 276, which may comprise thecondensable fluid in liquid phase. Liquid layer 276 may be in fluidcommunication with dehumidification region liquid inlet 272. At least aportion of chamber 270 not occupied by liquid layer 276 may comprise avapor distribution region 278, which may be in fluid communication withapparatus gas outlet 274. Dehumidification chamber 270 may also compriseweir 280, which may establish the maximum height of liquid layer 276.Second dehumidification stage 252 may be configured such that liquidflows across chamber 270 from dehumidification region liquid inlet 272to weir 280.

In operation, a first gas stream may enter vessel 294 of apparatus 200via apparatus gas inlet 208, which is in fluid communication with gasdistribution chamber 202. In gas distribution chamber 202, the first gasstream may be substantially homogeneously distributed throughout gasdistribution region 212, along the bottom surface of bubble generator226. The first gas stream may flow through bubble generator 226, therebyforming a plurality of gas bubbles. The gas bubbles may then flowthrough liquid layer 222, which may comprise a condensable fluid inliquid phase (e.g., liquid water) and one or more contaminants (e.g.,dissolved salts). As the gas bubbles flow through liquid layer 222,which may have a higher temperature than the gas bubbles, heat and/ormass (e.g., condensable fluid) may be transferred from liquid layer 222to the gas bubbles through an evaporation (e.g., humidification)process, such that the gas bubbles comprise the condensable fluid invapor phase. In some embodiments, the condensable fluid is water, andthe gas bubbles are at least partially humidified as they travel throughliquid layer 222. Bubbles of the at least partially humidified first gasmay enter vapor distribution region 224 of humidification chamber 220and recombine, resulting in the at least partially humidified first gasstream being substantially evenly distributed throughout vapordistribution region 224.

The at least partially humidified first gas stream may then enterhumidification chamber 236 of second humidification stage 218, flowingthrough bubble generator 244 and forming bubbles of the at leastpartially humidified first gas. The gas bubbles may then flow throughliquid layer 238, which may have a higher temperature than the gasbubbles. As the gas bubbles flow through liquid layer 238, they mayundergo an evaporation process, and heat and/or mass may be transferredfrom liquid layer 238 to the gas bubbles. After exiting liquid layer238, the gas bubbles may enter vapor distribution region 242 ofhumidification chamber 236, where they may recombine and form a furtherheated and humidified first gas stream that is substantiallyhomogeneously distributed throughout vapor distribution region 242,along the bottom surface of bubble generator 246.

The further humidified first gas stream may then enter firstdehumidification stage 250 of dehumidification region 206 through bubblegenerator 246. Bubbles of the further humidified first gas may travelthrough liquid layer 256, which may comprise the condensable fluid inliquid phase (e.g., substantially pure water). The temperature of liquidlayer 256 may be lower than the temperature of the bubbles of thefurther humidified first gas, and heat and/or mass (e.g., condensablefluid) may be transferred from the heated, humidified first gas bubblesto liquid layer 256 through a condensation (e.g., dehumidification)process to form an at least partially dehumidified gas. Bubbles of thecooled, at least partially dehumidified first gas may recombine in vapordistribution region 260 of dehumidification chamber 254. The recombinedcooled, at least partially dehumidified first gas may then enter seconddehumidification stage 252 through bubble generator 262. Bubbles of thecooled, at least partially dehumidified gas may travel through liquidlayer 276, which may have a lower temperature than the gas bubbles. Asthe gas bubbles travel through liquid layer 276, they may be furtherdehumidified, transferring heat and/or mass to liquid layer 276 througha condensation (e.g., dehumidification) process. Bubbles of the furtherdehumidified first gas may recombine in vapor distribution region 278 ofdehumidification chamber 270 and subsequently exit vessel 294 ofcombined bubble column apparatus 200 through apparatus gas outlet 274.

In some embodiments, one or more liquid streams flows through combinedbubble column apparatus 200 (e.g., in substantially the oppositedirection as the first gas stream). According to some embodiments, afirst liquid stream comprising the condensable fluid in liquid phase andone or more contaminants enters vessel 294 of apparatus 200 throughhumidification region liquid inlet 240, which is in fluid communicationwith liquid layer 238 of second humidification stage 218. As the firstliquid stream flows across chamber 236, from humidification regionliquid inlet 240 to weir 248, the first liquid stream (e.g., as part ofliquid layer 238) may directly contact a plurality of gas bubbles havinga temperature lower than the temperature of the first liquid stream.Heat and/or mass may be transferred from the first liquid stream to thegas bubbles through an evaporation (e.g., humidification) process,resulting in a cooled first liquid stream. If the height of liquid layer238 exceeds the height of weir 248, the cooled first liquid stream mayflow over the top of weir 248, through downcomer 228, to a pool ofliquid surrounding the outlet of downcomer 228. If the height of thepool of liquid exceeds the height of weir 232, the cooled first liquidstream may flow over the top of weir 232 to liquid layer 222 of firsthumidification stage 216. As the cooled first liquid stream flows acrosschamber 220 of first humidification stage 216, from weir 232 to weir234, the cooled first liquid stream (e.g., as part of liquid layer 222)may directly contact a plurality of gas bubbles having a temperaturelower than the cooled first liquid stream. Heat and/or mass may betransferred from the cooled first liquid stream to the gas bubblesthrough an evaporation process, resulting in a further cooled firstliquid stream. If the height of liquid layer 222 exceeds the height ofweir 234, the further cooled first liquid stream may flow over the topof weir 234, through downcomer 230, to liquid sump volume 214. Thefurther cooled first liquid stream may then exit vessel 294 of combinedbubble column apparatus 200 through humidification region liquid outlet210.

In some embodiments, a second liquid stream comprising the condensablefluid in liquid phase enters vessel 294 of apparatus 200 throughdehumidification region liquid inlet 272, which is in fluidcommunication with liquid layer 276 of second dehumidification stage252. As the second liquid stream flows across dehumidification chamber270, from dehumidification region liquid inlet 272 to weir 280, thesecond liquid stream (e.g., as part of liquid layer 276) may directlycontact a plurality of gas bubbles having a temperature higher than thetemperature of the second liquid stream. Heat and/or mass may betransferred from the gas bubbles to the second liquid stream, resultingin a heated second liquid stream. If the height of liquid layer 276exceeds the height of weir 280, the heated second liquid stream may flowover the top of weir 280, through downcomer 264, to a pool of liquidsurrounding the outlet of downcomer 264. If the height of the pool ofliquid exceeds the height of weir 266, the heated second liquid streammay flow over the top of weir 266 to liquid layer 256 of firstdehumidification stage 250. As the heated second liquid stream flowsacross chamber 254 of first dehumidification stage 250, from weir 266 toweir 268, the heated second liquid stream (e.g., as part of liquid layer256) may directly contact a plurality of gas bubbles having a highertemperature than the heated second liquid stream. Heat and/or mass maybe transferred from the gas bubbles to the second liquid stream,resulting in a further heated second liquid stream. If the height ofliquid layer 256 exceeds the height of weir 268, the further heatedsecond liquid stream may flow over the top of weir 268 and exit vessel294 of combined bubble column apparatus 200 through dehumidificationregion liquid outlet 258.

In certain embodiments, combined bubble column apparatus 200 furthercomprises one or more additional gas inlets. For example, in FIG. 2B,apparatus 200 further comprises optional second apparatus gas inlet 282.Second apparatus gas inlet 282 may be in fluid communication with asource of a second gas (not shown in FIG. 2B). The composition of thesecond gas may be the same or different as the first gas. In some cases,the second gas may comprise the condensable fluid in vapor phase (e.g.,water vapor) and/or a non-condensable gas. In some embodiments, thefirst and second gases may have different vapor (e.g., water vapor)concentrations. The first and second gases may, in certain cases, havesubstantially the same vapor concentration. In some cases, the first andsecond gases may be maintained at different temperatures. The differencebetween the temperatures of the first and second gases may, in certainembodiments, be at least about 1° C., at least about 5° C., at leastabout 10° C., at least about 20° C., at least about 50° C., at leastabout 100° C., at least about 150° C., or at least about 200° C. Incertain cases, the first and second gases may be maintained atsubstantially the same temperature.

In some embodiments, the one or more additional gas inlets are fluidlyconnected to one or more additional gas outlets of the combined bubblecolumn apparatus. As shown in FIG. 2C, combined bubble column apparatus200 may further comprise optional second apparatus gas outlet 284. Insome cases, second apparatus gas outlet 284 is fluidly connected tosecond apparatus gas inlet 282 via a gas conduit. In certain cases,second apparatus gas outlet 284 is in fluid communication with anintermediate humidification stage (e.g., not the final humidificationstage). In some embodiments, second apparatus gas inlet 282 is in fluidcommunication with an intermediate dehumidification stage (e.g., not thefirst dehumidification stage).

In some cases, extraction from at least one intermediate location in thehumidification region and injection into at least one intermediatelocation in the dehumidification region may be thermodynamicallyadvantageous. Because the portion of a gas flow exiting thehumidification region at an intermediate gas outlet (e.g., the extractedportion) has not passed through the entire humidification region, thetemperature of the gas flow at the intermediate gas outlet (e.g., outlet284) may be lower than the temperature of the gas flow at the main gasoutlet of the humidification region (e.g., bubble generator 246). Thelocations of the intermediate extraction points (e.g., gas outlets)and/or injection points (e.g., gas inlets) may be selected to increasethe thermal efficiency of the system. For example, because a gas (e.g.,air) may have increased vapor content at higher temperatures than atlower temperatures, and because the heat capacity of a gas with highervapor content may be higher than the heat capacity of a gas with lowervapor content, less gas may be used in higher temperature areas of thehumidification region and/or dehumidification region to better balancethe heat capacity rate ratios of the gas (e.g., air) and liquid (e.g.,water) streams. Extraction and/or injection of a portion of a gas flowat intermediate locations may therefore advantageously allow formanipulation of gas mass flows and for greater heat recovery.

However, it should be recognized that in some embodiments, under certainoperating conditions, intermediate extraction and/or injection may notnecessarily or always increase the thermal efficiency of a combined HDHapparatus (e.g., a combined bubble column apparatus). Additionally,there may be certain drawbacks associated with extraction and/orinjection at intermediate locations in some situations. For example,intermediate extraction and/or injection may reduce the condensablefluid (e.g., water) production rate of the apparatus, and there may becertain additional costs associated with intermediate extraction and/orinjection (e.g., costs associated with instrumentation, ducting,insulation, and/or droplet separation). In some cases, if thetemperature difference between a gas flow at an intermediate injectionlocation in the dehumidification region and a gas flow extracted fromthe humidification region and injected in the intermediate injectionlocation is too great, production rates and/or energy efficiency may bedecreased. Accordingly, in some cases, it may be advantageous to buildand/or operate an apparatus without intermediate extraction and/orinjection.

In some embodiments, a combined HDH apparatus (e.g., a combined bubblecolumn apparatus) further comprises additional components that mayenhance apparatus performance. For example, in certain embodiments, thecombined HDH apparatus comprises one or more optional dropleteliminators. As noted above, the presence of one or more dropleteliminators (e.g., extending across the opening of one or more gasoutlets) may advantageously reduce or eliminate droplet entrainment andmay thereby increase the amount of condensable fluid (e.g.,substantially pure water) recovered using the combined HDH apparatus. InFIG. 2D, combined bubble column apparatus 200 comprises a first dropleteliminator 286 positioned upstream of bubble generator 246, which actsas a gas outlet of humidification region 204. As shown in FIG. 2D,combined bubble column apparatus 200 further comprises a second dropleteliminator 290 positioned across the opening of apparatus gas outlet274, which acts as a gas outlet of dehumidification region 206.

According to some embodiments, the combined HDH apparatus (e.g.,combined bubble column apparatus) further comprises an optional liquidcollector. In some cases, the liquid collector is positioned between thehumidification region and the dehumidification region of the vessel ofthe combined HDH apparatus. As noted above, the presence of a liquidcollector may advantageously prevent any liquid (e.g., substantiallypure water) that falls from the dehumidification region from comminglingwith liquid from the humidification region (e.g., salt-containingwater). In FIG. 2D, combined bubble column apparatus 200 comprises aliquid collector 288 positioned between humidification region 204 anddehumidification region 206.

In some embodiments, the combined HDH apparatus (e.g., combined bubblecolumn apparatus) comprises an external liquid sump. In some cases, thepresence of an external liquid sump may advantageously reduce the weightof the dehumidification region and/or lower the center of mass of thecombined HDH apparatus. As shown in FIG. 2E, combined bubble columnapparatus 200 comprises external liquid sump 292, which is in fluidcommunication with dehumidification region liquid outlet 258.

While certain embodiments described above have been directed to acombined HDH apparatus (e.g., a combined bubble column apparatus)comprising a dehumidification region arranged vertically above ahumidification region, with each of the humidification anddehumidification regions comprising a plurality of vertically arrangedstages, the combined HDH apparatus may have any suitable structure orarrangement. For example, a humidification region and dehumidificationregion may be arranged vertically (e.g., the dehumidification regionpositioned above or below the humidification region) or horizontally(e.g., the dehumidification region positioned to the right or left ofthe humidification region) within a vessel of a combined HDH apparatus.In some cases, the humidification region and/or dehumidification regionof the combined HDH apparatus comprise a plurality of stages that arevertically arranged or horizontally arranged. In certain embodiments, acombined HDH apparatus comprises a vessel that comprises a verticallyarranged humidification region (e.g., comprising a plurality ofhorizontally or vertically arranged stages) and dehumidification region(e.g., comprising a plurality of horizontally or vertically arrangedstages). In some embodiments, a combined HDH apparatus comprises avessel that comprises a horizontally arranged humidification region(e.g., comprising a plurality of horizontally or vertically arrangedstages) and dehumidification region (e.g., comprising a plurality ofhorizontally or vertically arranged stages).

FIG. 3 shows a schematic illustration of an exemplary combined HDHapparatus (e.g., combined bubble column apparatus) comprising a vesselcomprising a humidification region positioned side-by-side with adehumidification region, according to some embodiments. In FIG. 3,apparatus 300 comprises vessel 350 comprising humidification region 302and dehumidification region 304 positioned to the left of humidificationregion 302. Humidification region 302 and dehumidification region 304each comprise a plurality of vertically arranged stages. As shown inFIG. 3, humidification region 302 comprises gas distribution chamber310, first stage 312 positioned above gas distribution chamber 310,second stage 314 positioned above first stage 312, third stage 316positioned above second stage 314, fourth stage 318 positioned abovethird stage 316, fifth stage 320 positioned above fourth stage 318, andsixth stage 322 positioned above fifth stage 320. Gas distributionchamber 310, which may be positioned at the bottom of humidificationregion 302, may be in fluid communication with apparatus gas inlet 306,humidification region liquid outlet 308, and/or first stage 312 (e.g.,through a bubble generator). In some cases, gas distribution chamber 310comprises a gas distribution region and a liquid sump volume. Sixthstage 322, which may be positioned at the top of humidification region302, may be in fluid communication with humidification region liquidinlet 324. In addition, sixth stage 322 may be in fluid communicationwith gas conduit 328 connecting humidification region 302 anddehumidification region 304. In some cases, droplet eliminator 326 maybe positioned between sixth stage 322 and gas conduit 328 to preventliquid droplets from entering gas conduit 328.

Gas conduit 328 may fluidly connect sixth stage 322 of humidificationregion 302 with gas distribution chamber 328 of dehumidification region304. As shown in FIG. 3, dehumidification region 304 comprises gasdistribution chamber 328, first stage 332 positioned above gasdistribution chamber 328, second stage 334 positioned above first stage332, third stage 336 positioned above second stage 334, fourth stage 338positioned above third stage 336, fifth stage 340 positioned abovefourth stage 338, and sixth stage 342 positioned above fifth stage 340.Gas distribution chamber 328, which may be positioned at the bottom ofdehumidification region 304, may be in fluid communication withdehumidification region liquid outlet 330 and/or first stage 332 (e.g.,through a bubble generator). In some cases, gas distribution chamber 328comprises a gas distribution region and a liquid sump volume. In FIG. 3,sixth stage 342, which is positioned at the top of dehumidificationregion 304, is in fluid communication with dehumidification regionliquid inlet 344 and apparatus gas outlet 348. In some cases, dropleteliminator 346 may be positioned between sixth stage 342 and gas outlet348 to prevent entrainment of liquid droplets from sixth stage 342.

In operation, a gas (e.g., a non-condensable gas) may enter combined HDHapparatus 300 through apparatus gas inlet 306. The gas may travelsequentially through each of stages 312, 314, 316, 318, 320, and 322 ofhumidification region 302. Each stage of humidification region 302 maycomprise a liquid layer comprising a condensable fluid in liquid phaseand one or more contaminants (e.g., dissolved salts). As the gas flowsthrough each stage of humidification region 302 and comes into contactwith each of the liquid layers, the gas may become increasingly heatedand humidified. The heated, humidified gas may then flow through dropleteliminator 326, into gas conduit 328. The heated, humidified gas mayflow through gas conduit 328 to gas distribution chamber 328 ofdehumidification region 304. The heated, humidified gas may subsequentlyflow through each of stages 332, 334, 336, 338, 340, and 342 ofdehumidification region 304. Each stage of dehumidification region 304may comprise a liquid layer comprising the condensable fluid in liquidphase. As the heated, humidified gas flows through each stage ofdehumidification region 304, the heated, humidified gas may becomeincreasingly cooled and dehumidified. The cooled, dehumidified gas maythen exit vessel 350 of combined HDH apparatus 300 through apparatus gasoutlet 348.

In some embodiments, two liquid streams may flow through combined HDHapparatus 300 in directions substantially opposite to the direction ofthe gas stream (e.g., counter-flow to the gas stream). In humidificationregion 302, a first liquid stream comprising a condensable fluid inliquid phase and one or more contaminants (e.g., salt-containing water)may enter sixth stage 322 of humidification region 302 (e.g., theuppermost stage of humidification region 302) through humidificationregion liquid inlet 324. The first liquid stream may then flowsequentially through each of stages 322, 320, 318, 316, 314, and 312 ofhumidification region 302. As the first liquid stream flows through eachstage, the first liquid stream may encounter gas bubbles having atemperature lower than the temperature of the first liquid stream. Heatand/or mass may be transferred from the first liquid stream to the gasbubbles, resulting in a cooled first liquid stream. After flowingthrough each of the stages of humidification region 302, the cooledfirst liquid stream may flow to gas distribution chamber 310 and exitvessel 350 of apparatus 300 through humidification region liquid outlet308.

In dehumidification region 304, a second liquid stream comprising thecondensable fluid in liquid phase (e.g., substantially pure water) mayenter sixth stage 342 of dehumidification region 304 throughdehumidification region liquid inlet 344. The second liquid stream maythen flow sequentially through each of stages 342, 340, 338, 336, 334,and 332 of dehumidification region 304. As the second liquid streamflows through each stage, the second liquid stream may encounter gasbubbles having a higher temperature than the temperature of the secondliquid stream. Heat and/or mass may be transferred from the gas bubblesto the second liquid stream, resulting in a heated second liquid stream.After flowing through each of the stages of dehumidification region 304,the heated second liquid stream may flow to gas distribution chamber 328and exit apparatus 300 through dehumidification region liquid outlet330.

In some embodiments, a combined HDH apparatus (e.g., a combined bubblecolumn apparatus) comprises a horizontally arranged humidificationregion and dehumidification region (e.g., positioned horizontallyadjacent to each other). In certain cases, the horizontally arrangedhumidification and dehumidification regions each comprise a plurality ofhorizontally arranged stages. According to some embodiments, anapparatus comprising a horizontally arranged humidification regioncomprising a plurality of horizontally arranged stages anddehumidification region comprising a plurality of horizontally arrangedstages advantageously has a lower height than an apparatus having otherconfigurations (e.g., a vertically arranged humidification region anddehumidification region, a horizontally arranged humidification anddehumidification region where at least one of the humidification anddehumidification regions comprises a plurality of vertically arrangedstages). In some embodiments, an apparatus comprising a horizontallyarranged humidification region comprising a plurality of horizontallyarranged stages and a dehumidification region comprising a plurality ofhorizontally arranged stages advantageously has a relatively smallfootprint. As used herein, a footprint generally refers to the surfacearea of a bottom surface of an apparatus (e.g., the surface in contactwith the ground). In certain cases, it may be advantageous for acombined HDH apparatus to have a relatively low height and/or arelatively small footprint. For example, a relatively low height and/orrelatively small footprint may advantageously facilitate shipping (e.g.,because the apparatus may fit on existing truck beds) and/orinstallation of the apparatus, particularly for systems located atremote sites.

According to some embodiments, the combined HDH apparatus (e.g.,combined bubble column apparatus) has a relatively low height. Forexample, in some embodiments, the combined HDH apparatus comprises avessel having a relatively low height. The height of a vessel may referto the maximum vertical distance between a first end (e.g., a top end)and a second end (e.g., a bottom end) of the vessel. Referring to FIG.1A, vessel 150 of apparatus 100 has a height H. In some cases, thevessel of the combined HDH apparatus has a height of about 5 m or less,about 4 m or less, about 3 m or less, about 2 m or less, about 1 m orless, or, in some cases, about 0.5 m or less. In certain cases, thevessel of the combined HDH apparatus has a height in the range of about1 m to about 5 m, about 1 m to about 4 m, about 1 m to about 3 m, orabout 1 m to about 2 m.

In some embodiments, the vessel of the combined HDH apparatus (e.g.,combined bubble column apparatus) has a relatively small footprint(e.g., surface area of a bottom surface of the vessel). In certainembodiments, the vessel of the combined HDH apparatus has a footprint ofabout 100 m² or less, about 75 m² or less, about 50 m² or less, about 20m² or less, about 10 m² or less, about 5 m² or less, about 2 m² or less,or about 1 m² or less. In some cases, the vessel of the combined HDHapparatus has a footprint in the range of about 1 m² to about 100 m²,about 1 m² to about 75 m², about 1 m² to about 50 m², about 1 m² toabout 20 m², about 1 m² to about 10 m², or about 1 m² to about 5 m².

FIG. 4 shows, according to some embodiments, a schematic cross-sectionalillustration of an exemplary combined bubble column apparatus comprisinga vessel comprising a humidification region positioned side-by-side witha dehumidification region, where both the humidification anddehumidification regions comprise horizontally arranged stages. In FIG.4, combined bubble column apparatus 400 comprises vessel 434 comprisinghumidification region 402 and dehumidification region 404, which ispositioned to the left of humidification region 402. As shown in FIG. 4,humidification region 402 comprises apparatus gas inlet 406,humidification region liquid inlet 408, and humidification region liquidoutlet 410. In addition, humidification region 402 comprises a pluralityof horizontally arranged stages 412A-D. Each of stages 412A-D comprisesa chamber comprising a liquid layer (e.g., one of liquid layers 414A-D)and a vapor distribution region above the liquid layer. Additionally,each of stages 412A-D further comprises a gas conduit (e.g., one of gasconduits 416A-D), and a bubble generator fluidly connected to the gasconduit (e.g., one of bubble generators 418A-D). As shown in FIG. 4, atleast a portion of the bubble generator of each stage is positionedbelow a top surface of the liquid layer of the stage, such that a gasflowing through the bubble generator generates gas bubbles that flowthrough the liquid layer of the stage. In a particular, non-limitingexample, bubble generator 418A extends from a top surface of liquidlayer 414A to a bottom surface of stage 412A. In certain embodiments,one or more bubble generators are positioned such that they extendacross a bottom surface of a liquid layer of a stage (e.g., such thatthe gas flows beneath the one or more bubble generators and gas bubblesflow upwards through the liquid layers). FIG. 4 further shows thatstages 412A-D are separated by a plurality of baffles 436A-C. In someembodiments, at least a portion of the baffles comprise a first end incontact with a top surface of a stage of humidification region 402 and asecond end submerged in a liquid layer of the stage. In some cases, oneor more gas conduits traverse one or more baffles. For example, in FIG.4, each of gas conduits 416B-D traverses (e.g., passes through) one ofbaffles 436A-C (e.g., gas conduit 416B traverses baffle 436A, gasconduit 416C traverses baffle 436B, gas conduit 416D traverses baffle436C). The baffles thus may prevent a gas flowing through humidificationregion 402 from bypassing gas conduits 416A-D and bubble generators418A-D. In FIG. 4, baffle 436D, which is traversed by gas conduit 430A,separates humidification region 402 from dehumidification region 404.

In FIG. 4, dehumidification region 404 comprises dehumidification regionliquid inlet 420, dehumidification region liquid outlet 422, andapparatus gas outlet 424. In addition, dehumidification region 404comprises a plurality of horizontally arranged stages 426A-D. Each ofstages 426A-D comprises a chamber comprising a liquid layer (e.g., oneof liquid layers 428A-D) and a vapor distribution region above theliquid layer. Each of stages 426A-D also comprises a gas conduit (e.g.,one of gas conduits 430A-D) and a bubble generator fluidly connected tothe gas conduit (e.g., one of bubble generators 432A-D). As in stages412A-D, in each of stages 426A-D, at least a portion of the bubblegenerator of the stage is positioned below a top surface of the liquidlayer of the stage. In certain embodiments, one or more bubblegenerators are positioned such that they extend across a bottom surfaceof a liquid layer of a stage (e.g., such that the gas flows beneath theone or more bubble generators and gas bubbles flow upwards through theliquid layers). As shown in FIG. 4, stages 426A-D are separated by aplurality of baffles 438A-C. In some embodiments, at least a portion ofthe baffles comprise a first end in contact with a top surface of astage of dehumidification region 404 and a second end submerged in aliquid layer of the stage (e.g., the baffle may extend at least from atop surface of a stage to a top surface of the liquid layer of thestage). In some cases, one or more gas conduits traverse one or morebaffles. For example, in FIG. 4, each of gas conduits 430B-D traversesone of baffles 438A-C (e.g., gas conduit 430B traverses baffle 438A, gasconduit 430C traverses baffle 438B, gas conduit 430D traverses baffle438C). Baffles 438A-C of dehumidification region 404 thus may prevent agas flowing through dehumidification region 404 from bypassing gasconduits 430A-D and bubble generators 432A-D.

In operation, a stream comprising a gas (e.g., a non-condensable gas)may flow through apparatus 400 in a first direction, and one or moreliquid streams may flow through apparatus 400 in a second, substantiallyopposite direction. For example, as shown in FIG. 4, a gas stream mayflow from right to left through apparatus 400, while a first liquidstream comprising a condensable fluid in liquid phase and one or morecontaminants (e.g., salt-containing water) may flow from left to rightthrough humidification region 402 and a second liquid stream comprisingthe condensable fluid in liquid phase (e.g., substantially pure water)may flow from left to right through dehumidification region 404. In FIG.4, the gas stream enters vessel 434 of apparatus 400 through apparatusgas inlet 406. The gas stream may enter first stage 412A ofhumidification region 402, flowing through gas conduit 416A to bubblegenerator 418A and forming a plurality of gas bubbles. The gas bubblesmay subsequently travel through liquid layer 414A, which may have ahigher temperature than the gas bubbles. In liquid layer 414A, heat andmass may be transferred from liquid layer 414A to the gas bubbles toproduce heated, at least partially humidified gas bubbles. Aftertraveling through liquid layer 414A, the gas bubbles may recombine inthe vapor distribution region of first stage 412A positioned aboveliquid layer 414, substantially evenly distributing throughout the vapordistribution region. The heated, at least partially humidified gasstream may then enter second stage 412B, flowing through gas conduit416B to bubble generator 418B. The gas stream may continue to flow fromright to left through humidification region 402, becoming increasinglyheated and humidified as it flows through each stage of humidificationregion 402.

After flowing through each of stages 412A-D of humidification region402, the heated, humidified gas stream may enter first stage 426A ofdehumidification region 404, flowing through gas conduit 430A to bubblegenerator 432A. Bubbles of the heated, humidified gas may be formed andmay travel through liquid layer 428A, which may have a lower temperaturethan the heated, humidified gas bubbles. In liquid layer 428A, heat andmass may be transferred from the heated, humidified gas bubbles toliquid layer 428A. The cooled, at least partially dehumidified gasbubbles may then recombine in the vapor distribution region of firststage 426A, and the cooled, at least partially dehumidified gas streammay flow through gas conduit 430B to bubble generator 432B of secondstage 426B. The cooled, at least partially dehumidified gas stream maycontinue to flow from right to left through dehumidification region 404,becoming increasingly cooled and dehumidified as it flows through eachstage of dehumidification region 404.

While the gas stream flows from right to left through apparatus 400, thefirst liquid stream comprising a condensable fluid in liquid phase andone or more contaminants (e.g., salt-containing water) may flow fromleft to right through humidification region 402. As shown in FIG. 4, thefirst liquid stream may enter humidification region 402 throughhumidification region liquid inlet 408, forming at least a portion ofliquid layer 414D of fourth stage 412D. In fourth stage 412D, heat andmass may be transferred from the first liquid stream in liquid layer414D to bubbles of the gas stream formed by bubble generator 418D, andthe first liquid stream may be cooled. In addition, due to condensablefluid (e.g., water vapor) being transferred from the first liquid streamto the bubbles of the gas stream, the first liquid stream may becomemore concentrated (e.g., the concentration of one or more contaminantsmay increase). As the first liquid stream flows through each of stages412C, 412B, and 412A of humidification region 402, the temperature ofthe first liquid stream may decrease, and the concentration of one ormore contaminants in the stream may increase. The cooled, concentratedliquid stream may then exit vessel 434 of apparatus 400 throughhumidification region liquid outlet 410.

The second liquid stream comprising the condensable fluid in liquidphase (e.g., substantially pure water) may also flow through vessel 434of apparatus 400, flowing from left to right through dehumidificationregion 404. In FIG. 4, the second liquid stream enters dehumidificationregion 404 through dehumidification region water inlet 420, forming atleast a portion of liquid layer 428D of fourth stage 426D. In fourthstage 426D, heat and mass may be transferred from heated, humidified gasbubbles to the second liquid stream. Accordingly, as the second liquidstream flows through each of stages 426D, 426C, 426B, and 426A ofdehumidification region 404, the temperature of the second liquid streammay increase, and the volume of the second liquid stream may alsoincrease. The heated second liquid stream may then exit vessel 434 ofapparatus 400 through dehumidification region liquid outlet 422.

Although certain embodiments of the combined HDH apparatus (e.g.,combined bubble column apparatus) described above comprise ahumidification region positioned to the right of a dehumidificationregion, with a gas stream flowing from right to left and a plurality ofliquid streams flowing from left to right, it should be recognized thatother configurations and other flow directions are also possible. Forexample, in an apparatus comprising a horizontally arrangedhumidification region and dehumidification region, the humidificationregion may be positioned to the right of the dehumidification region. Insome cases, a gas stream may flow from left to right, and one or moreliquid streams may flow from right to left.

According to some embodiments, the combined HDH apparatus (e.g.,combined bubble column apparatus) is substantially continuously operatedand/or configured to facilitate substantially continuous operation. Asused herein, a continuously-operated HDH apparatus (e.g., bubble columnapparatus) refers to an apparatus in which a liquid feed stream is fedto the apparatus at the same time that a desalinated liquid stream isproduced by the apparatus. In some cases, one or more liquid streams maybe in substantially continuous motion. For example, for bubble columnHDH systems, a liquid feed stream (e.g., a salt-containing water stream)may be fed to the combined bubble column apparatus, substantiallycontinuously flow through one or more stages of the humidificationregion and/or dehumidification region of the apparatus, and result in adesalinated liquid stream (e.g., a substantially pure water stream)subsequently being discharged from the apparatus. In some cases, acontinuously-operated apparatus may be associated with certainadvantages, including, but not limited to, increased uptime and/orenhanced energy performance.

In some embodiments, the combined HDH apparatus (e.g., combined bubblecolumn apparatus) is substantially transiently operated and/orconfigured to facilitate substantially transient operation (e.g., batchprocessing). As used herein, a transiently-operated HDH apparatus refersto an apparatus in which an amount of liquid (e.g., salt-containingwater) is introduced into the apparatus and remains in the apparatusuntil a certain condition (e.g., a certain salinity, a certain density)is reached. Upon satisfaction of the condition, the liquid is dischargedfrom the apparatus. In certain cases, transient operation may allowcleaning operations to be interspersed with production operations. Forexample, transient operation may be advantageous for systems comprisingfilter presses, bioreactors, and/or other systems that may requireperiodic cleaning. In some cases, transient operation may advantageouslyfacilitate processing of highly viscous liquids (e.g., sugar-containingfeedstock) that may be difficult to pump.

FIG. 5 shows a schematic illustration of an exemplary bubble columnapparatus configured for transient operation, according to someembodiments. In FIG. 5, combined bubble column apparatus 500 comprisesvessel 534 comprising humidification region 502 and dehumidificationregion 504. Humidification region 502 comprises humidification chamber510, which is partially occupied by liquid layer 512. In someembodiments, vapor distribution region 514 occupies at least a portionof humidification chamber 510 that is not occupied by liquid layer 512.According to some embodiments, liquid layer 512 comprises a condensablefluid in liquid phase and one or more contaminants (e.g.,salt-containing water). In some cases, liquid layer 512 is in contact(e.g., direct contact) with heating element 506. Heating element 506 maybe any type of device configured to transfer heat to a liquid, such asthe liquid of liquid layer 512. Non-limiting examples of suitableheating elements include an electric heater (e.g., an electric immersionheater), a heat exchanger (e.g., any type of heat exchanger describedherein), and/or a heat pump. In certain embodiments, the heating elementis a heat exchanger fluidly connected to a heat source. Examples ofsuitable heat sources include, but are not limited to, a hot waterboiler (e.g., a gas-fired hot water boiler), waste heat from anindustrial process (e.g., power generation), solar energy, and/or acooling element of one or more dehumidification regions.Dehumidification region 504, which is fluidly connected tohumidification region 502 through bubble generator 524 and to apparatusgas outlet 526, comprises dehumidification chamber 518, which ispartially occupied by liquid layer 520. In some embodiments, vapordistribution region 522 occupies at least a portion of dehumidificationchamber 518 that is not occupied by liquid layer 520. In some cases,liquid layer 520 comprises a condensable fluid in liquid phase (e.g.,substantially pure water). Liquid layer 520 may be in contact (e.g.,direct contact) with cooling element 508. Cooling element 508 may be anytype of device configured to remove heat from a liquid, such as theliquid of liquid layer 520. Non-limiting examples of suitable coolingelements include an electric chiller, a heat exchanger (e.g., any heatexchanger described herein), and/or a heat pump. In certain embodiments,the cooling element is a heat exchanger fluidly connected to a coldsource. Examples of suitable cold sources include, but are not limitedto, air (e.g., for an air-cooled heat exchanger), temperaturestratification in a body of water, and/or a ground-coupled heatexchanger (e.g., with or without a heat pump). As shown in FIG. 5,vessel 534 of apparatus 500 further comprises gas distribution chamber530, which is fluidly connected to apparatus gas inlet 528 and is alsofluidly connected to humidification region 502 through bubble generator516. Gas distribution chamber 530 comprises gas distribution region 532(e.g., the space within chamber 530 throughout which a gas may bedistributed). In certain embodiments, apparatus gas outlet 526 isfluidly connected to apparatus gas inlet 528 through a gas conduit(e.g., duct) (not shown in FIG. 5). According to certain embodiments, asingle device may act as both a heating element (e.g., heating element506) of a humidification region and a cooling element (e.g., coolingelement 508) of a dehumidification region. For example, in some cases, aheat pump may act as both a heating element and a cooling element. In aparticular, non-limiting example, both the heating element and thecooling element are heat exchangers. In some cases, an intermediatefluid may transfer heat between the heating element and the coolingelement.

In operation, an amount of liquid comprising the condensable fluid inliquid phase and one or more contaminants (e.g., salt-containing water)may be introduced into humidification region 502 of combined bubblecolumn apparatus 500, forming liquid layer 512. In some cases, an amountof the condensable fluid in liquid phase (e.g., substantially purewater) may also be introduced into dehumidification region 504 ofapparatus 500, forming liquid layer 520.

A gas (e.g., a non-condensable gas) may then enter apparatus 500 throughapparatus gas inlet 528. The gas may flow through gas distributionchamber 530, where the gas may be substantially homogeneouslydistributed throughout gas distribution region 532 of chamber 530, alongthe bottom surface of bubble generator 516. The gas may flow throughbubble generator 516, generating bubbles that travel through liquidlayer 512. As the gas bubbles flow through liquid layer 512, heat andmass may be transferred from liquid layer 512 to the gas bubbles throughan evaporation process, producing heated, humidified gas bubbles.Heating element 506, which is in contact (e.g., direct contact) withliquid layer 512, may replace thermal energy that is lost from liquidlayer 512 in the form of latent and sensible heat. The heated,humidified gas bubbles may recombine in vapor distribution region 514 ofhumidification chamber 510 and flow through bubble generator 524,generating heated, humidified gas bubbles that travel through liquidlayer 520 in dehumidification region 504. As the heated, humidified gasbubbles travel through liquid layer 520 in dehumidification region 504,heat and mass (e.g., condensable fluid in liquid phase) may betransferred from the heated, humidified gas bubbles to liquid layer 520,which has a lower temperature than the gas bubbles, through acondensation process. Cooling element 508, which is in contact (e.g.,direct contact) with liquid layer 520, may remove thermal energy fromliquid layer 520 to prevent or mitigate an increase in the temperatureof liquid layer 520. The bubbles of the at least partially dehumidifiedgas may recombine in vapor distribution region 522 of chamber 518 ofdehumidification region 504 and exit vessel 534 of apparatus 500 throughgas outlet 526.

The gas may continue to flow through vessel 534 of apparatus 500,transferring amounts of condensable fluid from liquid layer 512 ofhumidification region 502 to liquid layer 520 of dehumidification region504, until a certain condition is reached (e.g., the liquid of liquidlayer 512 reaches a certain salinity and/or density, liquid layer 520reaches a certain volume, etc.). In some cases, substantially no liquidis added to or removed from liquid layer 512 and/or 520 (other thanthrough the gas stream) until the condition is satisfied. In certainembodiments, at least a portion of liquid layer 520 is removed fromapparatus 500 prior to satisfaction of the condition (e.g., to preventthe volume of liquid layer 520 from exceeding the volume of chamber518). Upon satisfaction of the condition (e.g., termination of the batchprocess), the liquid of liquid layer 512 and/or the liquid of liquidlayer 520 may be discharged from apparatus 500.

In some embodiments, one or more stages of a humidification regionand/or dehumidification region of a combined HDH apparatus (e.g., acombined bubble column apparatus) have certain advantageouscharacteristics. Some of these characteristics may relate to the liquidlayers of one or more stages of the humidification region and/ordehumidification region. For example, in some cases, one or more stagesmay comprise liquid layers having relatively low heights.

As noted above, one or more stages of a humidification region ordehumidification region may comprise a liquid layer. In some cases, thecomposition of a liquid layer in a stage of the humidification regionmay be different from the composition of a liquid layer in a stage ofthe dehumidification region. For example, in the humidification region,the liquid layer may comprise a liquid comprising a condensable fluid inliquid phase and one or more contaminants (e.g., dissolved salts). Insome embodiments, the liquid layer of the humidification stage comprisessalt-containing water (e.g., brine). In some embodiments, the liquidlayer of the humidification stage comprises seawater, brackish water,water produced form an oil and/or gas extraction process, flowbackwater, and/or wastewater (e.g., industrial wastewater). In thedehumidification region, the liquid layer may comprise the condensablefluid in liquid phase (e.g., water). In certain embodiments, the liquidlayer of the dehumidification stage comprises the condensable fluid inliquid phase in substantially purified form (e.g., having a relativelylow level of contaminants). According to some embodiments, the liquidlayer of the dehumidification stage comprises substantially pure water.

In some embodiments, the height of the liquid layer in one or morestages of the humidification region and/or dehumidification region isrelatively low during operation of the combined HDH apparatus (e.g.,substantially continuous operation and/or substantially transientoperation). In some cases, the height of the liquid layer within a stagecan be measured vertically from the surface of the bubble generator thatcontacts the liquid layer to the top surface of the liquid layer.

Having a relatively low liquid layer height in at least one stage may,in some embodiments, advantageously result in a relatively low pressuredrop between the inlet and outlet of an individual stage. Withoutwishing to be bound by a particular theory, the pressure drop across agiven stage of the humidification region or dehumidification region maybe due, at least in part, to the hydrostatic head of the liquid in thestage that the gas has to overcome. Therefore, the height of the liquidlayer in a stage may be advantageously kept low to reduce the pressuredrop across that stage.

In addition, a relatively low liquid layer height may enhance heatand/or mass transfer. Without wishing to be bound by a particulartheory, in both the humidification region and the dehumidificationregion, the theoretical maximum amount of heat and/or mass transfer mayoccur under conditions where the gas reaches the same temperature as theliquid and the amount of vapor in the gas is exactly at the saturationconcentration. The total area available via the gas-liquid interface atthe bubble surfaces and the residence time of the bubble in the liquid,which is determined by the liquid layer height in each stage (althoughabove a minimum liquid layer height the performance is unaffected), maydetermine how close the heat and/or mass transfer gets to theaforementioned theoretical maximum. Therefore, it may be advantageous tomaintain the liquid layer height at the minimum required to operate thesystem without affecting performance. In some cases, the liquid layerheight is maintained at a height lower than the minimum height to reducethe energy associated with moving air through the system. Althoughhydrostatic head generally varies linearly with respect to liquid layerheight, heat and/or mass transfer efficiency may vary exponentially. Ithas been discovered in the context of this invention that conditions ina bubble column humidification region and/or dehumidification region mayapproach the maximum amount of heat and/or mass transfer at a liquidlayer height of about 1-2 inches.

In some embodiments, during operation of the combined HDH apparatus(e.g., substantially continuous operation and/or substantially transientoperation), the liquid layer within at least one stage of thehumidification region and/or dehumidification region has a height ofabout 0.1 m or less, about 0.09 m or less, about 0.08 m or less, about0.07 m or less, about 0.06 m or less, about 0.05 m or less, about 0.04 mor less, about 0.03 m or less, about 0.02 m or less, about 0.01 m orless, or, in some cases, about 0.005 m or less. In some embodiments,during operation of the combined HDH apparatus, the liquid layer withinat least one stage of the humidification region and/or dehumidificationregion has a height in the range of about 0 m to about 0.1 m, about 0 mto about 0.09 m, about 0 m to about 0.08 m, about 0 m to about 0.07 m,about 0 m to about 0.06 m, about 0 m to about 0.05 m, about 0 m to about0.04 m, about 0 m to about 0.03 m, about 0 m to about 0.02 m, about 0 mto about 0.01 m, about 0 m to about 0.005 m, about 0.005 m to about 0.1m, about 0.005 m to about 0.09 m, about 0.005 m to about 0.08 m, about0.005 m to about 0.07 m, about 0.005 m to about 0.06 m, about 0.005 m toabout 0.05 m, about 0.005 m to about 0.04 m, about 0.005 m to about 0.03m, about 0.005 m to about 0.02 m, or about 0.005 m to about 0.01 m. Insome embodiments, during operation of the combined HDH apparatus (e.g.,substantially continuous operation and/or substantially transientoperation), the liquid layer within each stage of the humidificationregion and/or dehumidification region has a height of about 0.1 m orless, about 0.09 m or less, about 0.08 m or less, about 0.07 m or less,about 0.06 m or less, about 0.05 m or less, about 0.04 m or less, about0.03 m or less, about 0.02 m or less, about 0.01 m or less, or, in somecases, about 0.005 m or less. In some embodiments, during operation ofthe combined HDH apparatus, the liquid layer within each stage of thehumidification region and/or dehumidification region has a height in therange of about 0 m to about 0.1 m, about 0 m to about 0.09 m, about 0 mto about 0.08 m, about 0 m to about 0.07 m, about 0 m to about 0.06 m,about 0 m to about 0.05 m, about 0 m to about 0.04 m, about 0 m to about0.03 m, about 0 m to about 0.02 m, about 0 m to about 0.01 m, about 0 mto about 0.005 m, about 0.005 m to about 0.1 m, about 0.005 m to about0.09 m, about 0.005 m to about 0.08 m, about 0.005 m to about 0.07 m,about 0.005 m to about 0.06 m, about 0.005 m to about 0.05 m, about0.005 m to about 0.04 m, about 0.005 m to about 0.03 m, about 0.005 m toabout 0.02 m, or about 0.005 m to about 0.01 m.

In certain embodiments, the ratio of the height of the liquid layer in astage of the humidification region or dehumidification region to thelength of the stage may be relatively low. The length of the stagegenerally refers to the largest internal cross-sectional dimension ofthe stage. In some embodiments, the ratio of the height of the liquidlayer within at least one stage of the humidification region and/ordehumidification region during operation of the combined HDH apparatus(e.g., substantially continuous operation and/or substantially transientoperation) to the length of the at least one stage is about 1.0 or less,about 0.8 or less, about 0.6 or less, about 0.5 or less, about 0.4 orless, about 0.2 or less, about 0.18 or less, about 0.16 or less, about0.15 or less, about 0.14 or less, about 0.12 or less, about 0.1 or less,about 0.08 or less, about 0.06 or less, about 0.05 or less, about 0.04or less, about 0.02 or less, about 0.01 or less, or, in some cases,about 0.005 or less. In some embodiments, the ratio of the height of theliquid layer within at least one stage of the humidification regionand/or dehumidification region during operation of the combined HDHapparatus to the length of the at least one stage is in the range ofabout 0.005 to about 1.0, about 0.005 to about 0.8, about 0.005 to about0.6, about 0.005 to about 0.5, about 0.005 to about 0.4, about 0.005 toabout 0.2, about 0.005 to about 0.18, about 0.005 to about 0.16, about0.005 to about 0.15, about 0.005 to about 0.14, about 0.005 to about0.12, about 0.005 to about 0.1, about 0.005 to about 0.08, about 0.005to about 0.06, about 0.005 to about 0.05, about 0.005 to about 0.04,about 0.005 to about 0.02, or about 0.005 to about 0.01. In someembodiments, the ratio of the height of the liquid layer within eachstage of the humidification region and/or dehumidification region duringoperation of the combined HDH apparatus (e.g., substantially continuousoperation and/or substantially transient operation) to the length ofeach corresponding stage is about 1.0 or less, about 0.8 or less, about0.6 or less, about 0.5 or less, about 0.4 or less, about 0.2 or less,about 0.18 or less, about 0.16 or less, about 0.15 or less, about 0.14or less, about 0.12 or less, about 0.1 or less, about 0.08 or less,about 0.06 or less, about 0.05 or less, about 0.04 or less, about 0.02or less, about 0.01 or less, or, in some cases, about 0.005 or less. Incertain embodiments, the ratio of the height of the liquid layer withineach stage of the humidification region and/or dehumidification regionduring operation of the combined HDH apparatus to the length of eachcorresponding stage is in the range of about 0.005 to about 1.0, about0.005 to about 0.8, about 0.005 to about 0.6, about 0.005 to about 0.5,about 0.005 to about 0.4, about 0.005 to about 0.2, about 0.005 to about0.18, about 0.005 to about 0.16, about 0.005 to about 0.15, about 0.005to about 0.14, about 0.005 to about 0.12, about 0.005 to about 0.1,about 0.005 to about 0.08, about 0.005 to about 0.06, about 0.005 toabout 0.05, about 0.005 to about 0.04, about 0.005 to about 0.02, orabout 0.005 to about 0.01.

In some embodiments, the height of an individual stage within thehumidification region and/or dehumidification region (e.g., measuredvertically from the bubble generator positioned at the bottom of thestage to the top of the chamber within the stage) may be relatively low.As noted above, reducing the height of one or more stages maypotentially reduce costs and/or potentially increase heat and masstransfer within the system. In some embodiments, the height of at leastone stage of the humidification region and/or dehumidification region isabout 0.5 m or less, about 0.4 m or less, about 0.3 m or less, about 0.2m or less, about 0.1 m or less, or, in some cases, about 0.05 m or less.In certain cases, the height of at least one stage of the humidificationregion and/or dehumidification region is in the range of about 0 m toabout 0.5 m, about 0 m to about 0.4 m, about 0 m to about 0.3 m, about 0m to about 0.2 m, about 0 m to about 0.1 m, about 0 m to about 0.05 m,about 0.05 m to about 0.5 m, about 0.05 m to about 0.4 m, about 0.05 mto about 0.3 m, about 0.05 m to about 0.2 m, or about 0.05 m to about0.1 m. In some embodiments, the height of each stage of thehumidification region and/or dehumidification region is about 0.5 m orless, about 0.4 m or less, about 0.3 m or less, about 0.2 m or less,about 0.1 m or less, or, in some cases, about 0.05 m or less. In certaincases, the height of each stage of the humidification region and/ordehumidification region is in the range of about 0 m to about 0.5 m,about 0 m to about 0.4 m, about 0 m to about 0.3 m, about 0 m to about0.2 m, about 0 m to about 0.1 m, about 0 m to about 0.05 m, about 0.05 mto about 0.5 m, about 0.05 m to about 0.4 m, about 0.05 m to about 0.3m, about 0.05 m to about 0.2 m, or about 0.05 m to about 0.1 m.

In some embodiments, the pressure drop across a stage (i.e. thedifference between inlet gas pressure and outlet gas pressure) for atleast one stage is about 200 kPa or less, about 150 kPa or less, about100 kPa or less, about 75 kPa or less, about 50 kPa or less, about 20kPa or less, about 15 kPa or less, about 10 kPa or less, about 5 kPa orless, or about 1 kPa or less. In certain cases, the pressure drop acrossat least one stage is in the range of about 1 kPa to about 5 kPa, about1 kPa to about 10 kPa, about 1 kPa to about 15 kPa, about 1 kPa to about20 kPa, about 1 kPa to about 50 kPa, about 1 kPa to about 75 kPa, about1 kPa to about 100 kPa, about 1 kPa to about 150 kPa, or about 1 kPa toabout 200 kPa. In some embodiments, the pressure drop across at leastone stage of the humidification region and/or dehumidification region issubstantially zero. In certain cases, the pressure drop across eachstage of the humidification region and/or dehumidification region isabout 200 kPa or less, about 150 kPa or less, about 100 kPa or less,about 75 kPa or less, about 50 kPa or less, about 20 kPa or less, about15 kPa or less, about 10 kPa or less, about 5 kPa or less, or about 1kPa or less. In certain embodiments, the pressure drop across each stageof the humidification region and/or dehumidification region is in therange of about 1 kPa to about 5 kPa, about 1 kPa to about 10 kPa, about1 kPa to about 15 kPa, about 1 kPa to about 20 kPa, about 1 kPa to about50 kPa, about 1 kPa to about 75 kPa, about 1 kPa to about 100 kPa, about1 kPa to about 150 kPa, or about 1 kPa to about 200 kPa. According tocertain embodiments, the pressure drop across each stage of thehumidification region and/or dehumidification region is substantiallyzero.

The stage of a humidification region or dehumidification region of acombined HDH apparatus (e.g., a combined bubble column apparatus) mayhave any shape suitable for a particular application. In someembodiments, at least one stage of a humidification region and/ordehumidification region has a cross-sectional shape that issubstantially circular, substantially elliptical, substantially square,substantially rectangular, substantially triangular, or irregularlyshaped. In some embodiments, at least one stage of a humidificationregion and/or dehumidification region has a relatively large aspectratio. As used herein, the aspect ratio of a stage refers to the ratioof the length of the stage to the width of the stage. The length of thestage may refer to the largest internal cross-sectional dimension of thestage (e.g., in a plane perpendicular to a vertical axis of the stage),and the width of the stage may refer to the largest cross-sectionaldimension of the stage (e.g., in a plane perpendicular to a verticalaxis of the stage) measured perpendicular to the length.

In some embodiments, at least one stage of a humidification regionand/or dehumidification region of a combined HDH apparatus (e.g., acombined bubble column apparatus) has an aspect ratio of at least about1.5, at least about 2, at least about 5, at least about 10, at leastabout 15, or at least about 20. In some embodiments, at least one stageof a humidification region and/or dehumidification region has an aspectratio in the range of about 1.5 to about 5, about 1.5 to about 10, about1.5 to about 15, about 1.5 to about 20, about 2 to about 5, about 2 toabout 10, about 2 to about 15, about 2 to about 20, about 5 to about 10,about 5 to about 15, about 5 to about 20, about 10 to about 15, about 10to about 20, or about 15 to about 20. In some embodiments, each stage ofa humidification region and/or dehumidification region of a combined HDHapparatus has an aspect ratio of at least about 1.5, at least about 2,at least about 5, at least about 10, at least about 15, or at leastabout 20. In some embodiments, each stage of a humidification regionand/or dehumidification region of a combined HDH apparatus has an aspectratio in the range of about 1.5 to about 5, about 1.5 to about 10, about1.5 to about 15, about 1.5 to about 20, about 2 to about 5, about 2 toabout 10, about 2 to about 15, about 2 to about 20, about 5 to about 10,about 5 to about 15, about 5 to about 20, about 10 to about 15, about 10to about 20, or about 15 to about 20.

In some embodiments, one or more weirs in one or more stages of ahumidification region and/or dehumidification region of a combined HDHapparatus (e.g., a combined bubble column apparatus) are positionedwithin a chamber of the stage so as to control or direct flow of aliquid (e.g., within one stage and/or between two or more stages).

In some embodiments, the maximum height of a liquid layer in one or morestages of a humidification region and/or dehumidification region may beset by one or more weirs. As used herein, a weir refers to a structurethat obstructs liquid flow in a stage. In some cases, a weir may bepositioned adjacent or surrounding a region of the chamber where liquidmay flow out of the chamber, for example, into a different chamberbelow. For example, if a weir is positioned upstream of a liquid outlet,any additional liquid that would cause the height of a liquid layer toexceed the height of the weir would flow over the weir and exit thestage through the liquid outlet.

In some embodiments, one or more weirs create a pool of liquidsurrounding an outlet of a liquid conduit between two stages. In someembodiments, a weir is positioned adjacent or surrounding a region ofthe stage that receives a stream of liquid from, for example, adifferent chamber above the region or adjacent to the region. Forexample, a first stage may be positioned vertically below a secondstage, and the liquid outlet of the second stage may be a downcomer thatfeeds into the first stage. A weir may be positioned immediatelydownstream of the downcomer, such that the weir either encircles thedowncomer or extends all the way to the walls of the chamber to create apool in which the outlet of the downcomer is submerged. The pool mayprevent air from entering the downcomer. In some cases, the height ofthe pool is greater than the height of the liquid layer in the firststage (e.g., the height of the weir is greater than the height of theliquid layer in the first stage). Otherwise, the hydrostatic head forair sparging through the liquid layer in the first stage would begreater than the hydrostatic head required for air to flow up thedowncomer. Accordingly, a pool height greater than the height of theliquid layer in the first stage may advantageously prevent air fromflowing up the downcomer. In some embodiments, as additional liquid isintroduced into the pool and the height of the liquid in the poolexceeds the height of the weir, excess liquid may flow over the top ofthe weir (e.g., into the liquid layer of the first stage). In certainembodiments, the distance (e.g., vertical distance) between the top of aweir creating a pool encircling a downcomer and the bottom of an outletof the downcomer is greater than the height of the liquid layer in thesecond stage. In some cases, this may advantageously prevent back flowthrough the downcomer.

In some cases, a weir may be positioned within a chamber so as to notcontact one or more walls of the chamber. In some cases, a weir may bepositioned within a chamber so as to contact one or more walls of thechamber.

The one or more weirs may be selected to have a height that is less thanthe height of the chamber. In some embodiments, the height of the weirsmay determine the maximum height for a liquid layer in the chamber. Forexample, if a liquid layer residing in a first chamber reaches a heightthat exceeds the height of a weir positioned along a bottom surface ofthe chamber, then at least a portion of the excess liquid may flow overthe weir. In some cases, the excess liquid may flow into a second,adjacent chamber, e.g., a chamber positioned below the first chamber. Insome embodiments, at least one weir in a chamber has a height of about0.1 m or less, about 0.09 m or less, about 0.08 m or less, about 0.07 mor less, about 0.06 m or less, about 0.05 m or less, about 0.04 m orless, about 0.03 m or less, about 0.02 m or less, about 0.01 m or less,or, in some cases, about 0.005 m or less. In some embodiments, at leastone weir in a chamber has a height in the range of about 0 m to about0.1 m, about 0 m to about 0.09 m, about 0 m to about 0.08 m, about 0 mto about 0.07 m, about 0 m to about 0.06 m, about 0 m to about 0.05 m,about 0 m to about 0.04 m, about 0 m to about 0.03 m, about 0 m to about0.02 m, about 0 m to about 0.01 m, about 0 m to about 0.005 m, about0.005 m to about 0.1 m, about 0.005 m to about 0.09 m, about 0.005 m toabout 0.08 m, about 0.005 m to about 0.07 m, about 0.005 m to about 0.06m, about 0.005 m to about 0.05 m, about 0.005 m to about 0.04 m, about0.005 m to about 0.03 m, about 0.005 m to about 0.02 m, or about 0.005 mto about 0.01 m. In some embodiments, each weir in a chamber has aheight of about 0.1 m or less, about 0.09 m or less, about 0.08 m orless, about 0.07 m or less, about 0.06 m or less, about 0.05 m or less,about 0.04 m or less, about 0.03 m or less, about 0.02 m or less, about0.01 m or less, or, in some cases, about 0.005 m or less. In someembodiments, each weir in a chamber has a height in the range of about 0m to about 0.1 m, about 0 m to about 0.09 m, about 0 m to about 0.08 m,about 0 m to about 0.07 m, about 0 m to about 0.06 m, about 0 m to about0.05 m, about 0 m to about 0.04 m, about 0 m to about 0.03 m, about 0 mto about 0.02 m, about 0 m to about 0.01 m, about 0 m to about 0.005 m,about 0.005 m to about 0.1 m, about 0.005 m to about 0.09 m, about 0.005m to about 0.08 m, about 0.005 m to about 0.07 m, about 0.005 m to about0.06 m, about 0.005 m to about 0.05 m, about 0.005 m to about 0.04 m,about 0.005 m to about 0.03 m, about 0.005 m to about 0.02 m, or about0.005 m to about 0.01 m.

In some embodiments, one or more weirs may be positioned to promote theflow of a liquid across the length of the chamber in a substantiallylinear path. For example, the chamber may be selected to have across-sectional shape having a length that is greater than its width(e.g., a substantially rectangular cross-section), such that the weirspromote flow of liquid along the length of the chamber. In some cases,it may be desirable to promote such cross flow across a chamber tomaximize the interaction, and therefore heat and/or mass transfer,between the liquid phase and the vapor phase of a condensable fluid.

The HDH apparatuses (e.g., bubble column apparatuses) described hereinmay further include one or more components positioned to facilitate,direct, or otherwise affect flow of a fluid within the apparatus. Insome embodiments, at least one chamber of at least one stage of acombined HDH apparatus may include one or more baffles positioned todirect flow of a fluid, such as a stream of the condensable fluid inliquid phase (e.g., water). In certain cases, each chamber of thecombined HDH apparatus may comprise one or more baffles. Suitablebaffles for use in embodiments described herein include plate-likearticles having, for example, a substantially rectangular shape. Bafflesmay also be referred to as barriers, dams, or the like.

The baffle, or combination of baffles, may be arranged in variousconfigurations so as to direct the flow of a liquid within the chamber.In some cases, the baffle(s) can be arranged such that liquid travels ina substantially linear path from one end of the chamber to the other endof the chamber (e.g., along the length of a chamber having asubstantially rectangular cross-section). In some cases, the baffle(s)can be arranged such that liquid travels in a non-linear path across achamber, such as a path having one or more bends or turns within thechamber. That is, the liquid may travel a distance within the chamberthat is longer than the length of the chamber. In some embodiments, oneor more baffles may be positioned along a bottom surface of at least onechamber within a combined HDH apparatus, thereby affecting the flow ofliquid that enters the chamber.

In some embodiments, a baffle may be positioned in a manner so as todirect flow of a liquid within a single chamber, e.g., along a bottomsurface of a chamber in either a linear or non-linear manner. In someembodiments, one or more baffles may be positioned substantiallyparallel to the transverse sides (i.e., width) of a chamber having asubstantially rectangular cross-sectional shape, i.e., may be atransverse baffle. In some embodiments, one or more baffles may bepositioned substantially parallel to the longitudinal sides (i.e.,length) of a chamber having a substantially rectangular cross-sectionalshape, i.e., may be a longitudinal baffle. In such configurations, oneor more longitudinal baffles may direct the flow of liquid along asubstantially non-linear path.

In some embodiments, one or more baffles may be positioned in a mannerso as to direct flow of a liquid within a single chamber along a paththat may promote efficiency of heat and/or mass transfer. For example, achamber may comprise a liquid entering through a liquid inlet at a firsttemperature and a gas entering through a bubble generator at a second,different temperature. In certain cases, heat and mass transfer betweenthe liquid and the gas may be increased when the first temperatureapproaches the second temperature. One factor that may affect theability of the first temperature to approach the second temperature maybe the amount of time the liquid spends flowing through the chamber.

In some cases, it may be advantageous for portions of the liquid flowingthrough the chamber to spend substantially equal amounts of time flowingthrough the chamber. For example, heat and mass transfer may undesirablybe reduced under conditions where a first portion of the liquid spends ashorter amount of time in the chamber and a second portion of the liquidspends a longer amount of time in the chamber. Under such conditions,the temperature of a mixture of the first portion and the second portionmay be further from the second temperature of the gas than if both thefirst portion and the second portion had spent a substantially equalamount of time in the chamber. Accordingly, in some embodiments, one ormore baffles may be positioned in the chamber to facilitate liquid flowsuch that portions of the liquid flowing through the chamber spendsubstantially equal amounts of time flowing through the chamber. Forexample, one or more baffles within the chamber may spatially separateliquid located at the inlet (e.g., liquid likely to have spent a shorteramount of time in the chamber) from liquid located at the outlet (e.g.,liquid likely to have spent a longer amount of time in the chamber). Insome cases, one or more baffles within the chamber may facilitate liquidflow along flow paths having substantially the same length. For example,the one or more baffles may prevent a first portion of liquid fromtravelling along a substantially shorter path from the inlet of thechamber to the outlet of the chamber (e.g., along the width of a chamberhaving a rectangular cross section) and a second portion of liquid fromtravelling along a substantially longer path from the inlet of thechamber to the outlet of the chamber (e.g., along the length of achamber having a rectangular cross section).

In some cases, it may be advantageous to increase the amount of time aliquid spends flowing through a chamber. Accordingly, in certainembodiments, one or more baffles may be positioned within a singlechamber to facilitate liquid flow along a flow path having a relativelyhigh aspect ratio (e.g., the ratio of the average length of the flowpath to the average width of the flow path). For example, in some cases,one or more baffles may be positioned such that liquid flowing throughthe chamber follows a flow path having an aspect ratio of at least about1.5, at least about 2, at least about 5, at least about 10, at leastabout 20, at least about 50, at least about 75, at least about 100, ormore. In some embodiments, liquid flowing through the chamber follows aflow path having an aspect ratio in the range of about 1.5 to about 5,about 1.5 to about 10, about 1.5 to about 20, about 1.5 to about 50,about 1.5 to about 75, about 1.5 to about 100, about 5 to about 10,about 5 to about 20, about 5 to about 50, about 5 to about 75, about 5to about 100, about 10 to about 20, about 10 to about 50, about 10 toabout 75, about 10 to about 100, or about 50 to about 100.

In some cases, the aspect ratio of a liquid flow path through a chambermay be larger than the aspect ratio of the chamber. In certain cases,the presence of baffles to increase the aspect ratio of a liquid flowpath may facilitate the use of an apparatus having a relatively lowaspect ratio (e.g., about 1), such as an apparatus having asubstantially circular cross section. For example, FIG. 6A shows,according to some embodiments, a schematic illustration of an exemplarychamber 600 having a substantially circular cross section (e.g., bottomsurface) and a spiral baffle 602, according to some embodiments. Inoperation, liquid may enter chamber 600 through a liquid inlet (notshown) positioned at or near the center of the substantially circularcross section. The liquid may then flow along spiral baffle 602 and exitchamber 600 through a liquid outlet (not shown) positioned at the upperedge of the substantially circular cross section. While thesubstantially circular cross section of chamber 600 has an aspect ratioof about 1, the aspect ratio of the liquid flow path is substantiallygreater than 1 (e.g., approximately 4.5). As an additional example, FIG.6B shows, according to some embodiments, a schematic illustration of anexemplary chamber 600 having a substantially circular cross section(e.g., bottom surface) and comprising a first baffle 602 and a secondbaffle 604. In operation, liquid may enter chamber 600 through a liquidinlet (not shown) located in the upper left portion of the substantiallycircular cross section. The liquid may first flow in the direction ofarrow 606. The liquid may then flow around baffle 602 and flow in theopposite direction, in the direction of arrow 608. The liquid may thenflow around baffle 604 and flow in the direction of arrow 610 andsubsequently exit chamber 600 through a liquid outlet (not shown)located in the lower right portion of the substantially circular crosssection. While the aspect ratio of the circular cross section of chamber600 is about 1, the aspect ratio of the liquid flow path through chamber600 is substantially greater than 1.

In some embodiments, the baffle is a longitudinal baffle. For example, alongitudinal baffle may extend along the length of a stage, from a firstend to a second, opposing end. In some embodiments, there may be a gapbetween the longitudinal baffle and the first end and/or the second endof the stage, such that a liquid may flow around the longitudinal baffle(e.g., in a serpentine path). In some embodiments, a stage may comprisemore than one longitudinal baffle. In some embodiments, at least onelongitudinal baffle, at least two longitudinal baffles, at least threelongitudinal baffles, at least four longitudinal baffles, at least fivelongitudinal baffles, at least ten longitudinal baffles, or more, arearranged within the chamber. In some embodiments, the chamber includes1-10 longitudinal baffles, 1-5 longitudinal baffles, or, 1-3longitudinal baffles.

In some embodiments, the baffle is a transverse baffle (e.g., ahorizontal baffle). In some cases, at least one transverse baffle, atleast two transverse baffles, at least three transverse baffles, atleast four transverse baffles, at least five transverse baffles, atleast ten transverse baffles, or more, are arranged within the chamber.In some embodiments, the chamber includes 1-10 transverse baffles, 1-5transverse baffles, or, 1-3 transverse baffles.

The combined HDH apparatus (e.g., combined bubble column apparatus) maycomprise a vessel having any shape suitable for a particularapplication. In some embodiments, the vessel of the combined HDHapparatus has a cross section that is substantially circular,substantially elliptical, substantially square, substantiallyrectangular, substantially triangular, or irregularly shaped. It hasbeen recognized that it may be advantageous, in certain cases, for thevessel of a combined HDH apparatus to have a substantially circularcross section. In some cases, a vessel having a substantially circularcross section (e.g., a substantially cylindrical vessel) may be easierto manufacture than a vessel having a cross section of a different shape(e.g., a substantially rectangular cross section). For example, for asubstantially cylindrical vessel of a combined HDH apparatus having acertain diameter (e.g., about 0.6 m or less), prefabricated pipes and/ortubes may be used to form the walls of the vessel of the HDH apparatus.In addition, a substantially cylindrical vessel of a combined HDHapparatus may be manufactured from a sheet material (e.g., stainlesssteel) by bending the sheet and welding a single seam. In contrast, avessel of a combined HDH apparatus having a cross section of a differentshape may have more than one welded seam (e.g., a combined HDH apparatushaving a substantially rectangular cross section may have four weldedseams). Further, a vessel of a combined HDH apparatus having asubstantially circular cross section may require less material tofabricate than a combined HDH apparatus having a cross section of adifferent shape (e.g., a substantially rectangular cross section). Incertain embodiments, the vessel of the combined HDH apparatus has asubstantially parallelepiped shape, a substantially rectangularprismatic shape, a substantially cylindrical shape, a substantiallypyramidal shape, and/or an irregular shape. In some cases, it may beadvantageous for a vessel of a combined HDH apparatus (e.g., a combinedbubble column apparatus) to have a relatively high aspect ratio. Forexample, in some cases, it may be advantageous for a vessel of acombined HDH apparatus to have a substantially rectangular crosssection.

The vessel of the combined HDH apparatus (e.g., combined bubble columnapparatus) may have any size suitable for a particular application. Insome embodiments, the maximum cross-sectional dimension of the vessel ofthe combined HDH apparatus is about 10 m or less, about 5 m or less,about 2 m or less, about 1 m or less, about 0.5 m or less, or about 0.1m or less. In some cases, the vessel of the combined HDH apparatus has amaximum cross-sectional dimension ranging from about 0.01 m to about 10m, about 0.01 m to about 5 m, about 0.01 m to about 1 m, about 0.5 m toabout 10 m, about 0.5 m to about 5 m, about 0.5 m to about 1 m, about 1m to about 5 m, or about 1 m to about 10 m.

The exterior of the combined HDH apparatus (e.g., combined bubble columnapparatus) may comprise any suitable material. In certain embodiments,the vessel of the combined HDH apparatus comprises stainless steel,aluminum, and/or a plastic (e.g., polyvinyl chloride, polyethylene,polycarbonate). In some embodiments, it may be advantageous to minimizeheat loss from the vessel of the combined HDH apparatus to theenvironment. In some cases, the exterior and/or the interior of thevessel of the apparatus may comprise a thermally insulating material.For example, the vessel of the apparatus may be at least partiallycoated, covered, or wrapped with a thermally insulating material.Non-limiting examples of suitable thermally insulating materials includeelastomeric foam, fiberglass, ceramic fiber mineral wool, glass mineralwool, phenolic foam, polyisocyanurate, polystyrene, and polyurethane.

Some aspects are directed to a desalination system comprising a combinedHDH apparatus (e.g., a combined bubble column apparatus) fluidlyconnected to one or more additional devices. For example, in someembodiments, a desalination system comprises a combined HDH apparatus,as described herein, in fluid communication with a heat exchanger. Incertain cases, the heat exchanger facilitates transfer of heat from afluid stream flowing through a dehumidification region of the combinedHDH apparatus (e.g., a dehumidification region liquid outlet stream) toa fluid stream flowing through a humidification region of the combinedHDH apparatus (e.g., a humidification region liquid inlet stream). Forexample, the heat exchanger may advantageously allow energy to berecovered from a dehumidification region liquid outlet stream and usedto pre-heat a humidification region liquid inlet stream prior to entryof the humidification region liquid inlet stream into the humidificationregion of an exemplary combined HDH apparatus. This may, for example,avoid the need for an additional heating device to heat thehumidification region liquid inlet stream. Alternatively, if a heatingdevice is used, the presence of a heat exchanger to recover energy fromthe dehumidification region liquid outlet stream may reduce the amountof heat required to be applied to the humidification region liquid inletstream. The system can be configured such that the cooleddehumidification region liquid outlet stream can be returned to thedehumidification region through a liquid inlet and be re-used as aliquid to form liquid layers in the stage(s) of the dehumidificationregion. In this manner, the temperature of the liquid layers within thedehumidification region of the combined HDH apparatus can be regulatedsuch that, in each stage, the temperature of the liquid layer ismaintained at a temperature lower than the temperature of the gas.

In some embodiments, the heat exchanger is an external heat exchanger(e.g., external to the vessel of the combined HDH apparatus). In somecases, an external heat exchanger may be associated with certainadvantages. For example, the use of an external heat exchanger with acombined HDH apparatus may advantageously allow the apparatus to havereduced dimensions and/or reduced liquid layer heights within one ormore stages of a humidification region and/or dehumidification region ofthe apparatus. In some embodiments, the heat exchanger is an internalheat exchanger. For example, the internal heat exchanger may comprise atube coil located within a dehumidification region of a combined bubblecolumn apparatus. The tube coil may be positioned such that at least aportion of the tube coil is in thermal contact with a liquid layerwithin a stage of the dehumidification region. For example, in adehumidification region (e.g., bubble column dehumidification region)comprising a plurality of stages, each stage comprising a liquid layer,the tube coil may be positioned such that each liquid layer is inthermal contact with at least a portion of the tube coil. In some cases,a coolant (e.g., a humidification region liquid inlet stream) may flowthrough the internal heat exchanger (e.g., the tube coil), and heat maybe transferred from the liquid layer(s) of the dehumidification regionto the coolant.

FIG. 7A shows a schematic diagram of an exemplary embodiment ofdesalination system 700 comprising combined HDH (e.g. bubble column)apparatus 702 and external heat exchanger 708. Combined HDH apparatus702 may comprise vessel 714 comprising humidification region 704 anddehumidification region 706. As shown in FIG. 7A, dehumidificationregion 706 is fluidly connected to external heat exchanger 708 throughliquid conduit 710. In some cases, humidification region 704 is fluidlyconnected to external heat exchanger 708 through liquid conduit 712. Itshould be noted that in certain embodiments, humidification region 704is not connected to external heat exchanger 708, and an external coolingfluid may flow through heat exchanger 708 instead.

In operation, a dehumidification region liquid outlet stream containingan amount of absorbed heat may exit dehumidification region 706 viaconduit 710 at a temperature T₁ and enter external heat exchanger 708,flowing in a first direction. A humidification region liquid outletstream may exit humidification region 704 via conduit 712 at atemperature T₂ and enter external heat exchanger 708, flowing in asecond direction that is substantially opposite to the first direction(e.g., counter-flow). Heat may be transferred from the dehumidificationregion liquid stream to the humidification region liquid stream withinheat exchanger 708. The dehumidification region liquid stream may thenexit heat exchanger 708 at a temperature T₃, where T₃ is less than T₁,and the humidification region liquid stream may exit heat exchanger 708at a temperature T₄, where T₄ is greater than T₂. In some cases, thehumidification region liquid stream and dehumidification region liquidstream may flow in substantially parallel directions through heatexchanger 708. In other embodiments, the humidification region liquidstream and dehumidification region liquid stream may flow insubstantially non-parallel directions (e.g., opposite) directionsthrough heat exchanger 708.

As noted above, in some embodiments, humidification region 704 is notfluidly connected to heat exchanger 708. In addition, although FIG. 7Ashows liquid conduit 712 fluidly connecting an outlet of humidificationregion 704, heat exchanger 708, and an inlet of humidification region704, such that a stream exits humidification region 704, flows throughheat exchanger 708, and returns to humidification region 704, in somecases, system 700 is instead configured such that heat exchanger 708 isfluidly connected to a source of a liquid comprising one or morecontaminants (not shown). In some cases, liquid exiting humidificationregion 704 does not flow through heat exchanger 708.

Any heat exchanger known in the art may be used. Examples of suitableheat exchangers include, but are not limited to, plate-and-frame heatexchangers, shell-and-tube heat exchangers, tube-and-tube heatexchangers, plate heat exchangers, plate-and-shell heat exchangers,spiral heat exchangers, and the like. In a particular embodiment, theheat exchanger is a plate-and-frame heat exchanger. The heat exchangermay be configured such that a first fluid stream and a second fluidstream flow through the heat exchanger. In some cases, the first fluidstream and the second fluid stream may flow in substantially the samedirection (e.g., parallel flow), substantially opposite directions(e.g., counter flow), or substantially perpendicular directions (e.g.,cross flow). The first fluid stream may comprise, in certain cases, afluid stream that flows through a dehumidification region (e.g., adehumidification region liquid stream). In some embodiments, the secondfluid stream may comprise a coolant. The first fluid stream and/or thesecond fluid stream may comprise a liquid. In some embodiments, the heatexchanger may be a liquid-to-liquid heat exchanger. In some cases, morethan two fluid streams may flow through the heat exchanger.

The coolant may be any fluid capable of absorbing and transferring heat.Typically, the coolant is a liquid. The coolant may, in someembodiments, include water. In certain cases, the coolant may includesalt-containing water. For example, in a humidification-dehumidificationsystem, the coolant stream in the heat exchanger may be used to preheatsalt-containing water prior to entry into a humidification region (e.g.,the coolant stream may comprise the humidification region liquid inletstream).

In some embodiments, the heat exchanger may exhibit relatively high heattransfer rates. In some embodiments, the heat exchanger may have a heattransfer coefficient of at least about 150 W/(m² K), at least about 200W/(m² K), at least about 500 W/(m² K), at least about 1000 W/(m² K), atleast about 2000 W/(m² K), at least about 3000 W/(m² K), at least about4000 W/(m² K), or, in some cases, at least about 5000 W/(m² K). In someembodiments, the heat exchanger may have a heat transfer coefficient inthe range of at least about 150 W/(m² K) to at least about 5000 W/(m²K), at least about 200 W/(m² K) to about 5000 W/(m² K), at least about500 W/(m² K) to about 5000 W/(m² K), at least about 1000 W/(m² K) toabout 5000 W/(m² K), at least about 2000 W/(m² K) to about 5000 W/(m²K), at least about 3000 W/(m² K) to about 5000 W/(m² K), or at leastabout 4000 W/(m² K) to about 5000 W/(m² K).

In some embodiments, the heat exchanger may increase the temperature ofone or more fluid streams (e.g., the humidification region liquid inletstream) flowing through the heat exchanger and/or decrease thetemperature of one or more fluid streams (e.g., the dehumidificationregion liquid outlet stream) flowing through the heat exchanger. Forexample, the difference between the temperature of a fluid entering theheat exchanger and the fluid exiting the heat exchanger may be at leastabout 5° C., at least about 10° C., at least about 15° C., at leastabout 20° C., at least about 30° C., at least about 40° C., at leastabout 50° C., at least about 60° C., at least about 70° C., at leastabout 80° C., at least about 90° C., or at least about 100° C. In someembodiments, the difference between the temperature of a fluid enteringthe heat exchanger and the fluid exiting the heat exchanger may be inthe range of about 5° C. to about 20° C., about 5° C. to about 30° C.,about 5° C. to about 50° C., about 5° C. to about 60° C., about 5° C. toabout 90° C., about 5° C. to about 100° C., about 10° C. to about 30°C., about 10° C. to about 60° C., about 10° C. to about 90° C., about10° C. to about 100° C., about 20° C. to about 60° C., about 20° C. toabout 90° C., about 20° C. to about 100° C., about 30° C. to about 60°C., about 30° C. to about 90° C., about 30° C. to about 100° C., about60° C. to about 90° C., about 60° C. to about 100° C., or about 80° C.to about 100° C.

In some embodiments, an optional external heating device may be arrangedin fluid communication with the combined HDH apparatus (e.g., combinedbubble column apparatus) and/or the external heat exchanger. In certaincases, the heating device may be arranged such that, in operation, aliquid stream (e.g., a heat exchanger outlet stream, a humidificationregion liquid inlet stream) is heated in the heating device prior toentering the humidification region of the combined HDH apparatus. Insome embodiments, the heating device may be arranged such that adehumidification region liquid outlet stream is heated in the heatingdevice prior to entering the heat exchanger. Such an arrangement mayadvantageously increase the amount of heat transferred from thedehumidification region liquid outlet stream to another fluid streamflowing through the heat exchanger (e.g., a humidification region liquidinlet stream).

The heating device may be any device that is capable of transferringheat to a fluid stream. In some cases, the heating device is a heatexchanger. Any heat exchanger known in the art may be used. Examples ofsuitable heat exchangers include, but are not limited to,plate-and-frame heat exchangers, shell-and-tube heat exchangers,tube-and-tube heat exchangers, plate heat exchangers, plate-and-shellheat exchangers, and the like. In a particular embodiment, the heatexchanger is a plate-and-frame heat exchanger. The heat exchanger may beconfigured such that a first fluid stream and a second fluid stream flowthrough the heat exchanger. In some cases, the first fluid stream andthe second fluid stream may flow in substantially the same direction(e.g., parallel flow), substantially opposite directions (e.g., counterflow), or substantially perpendicular directions (e.g., cross flow). Thefirst fluid stream and/or the second fluid stream may comprise a liquid.In some embodiments, the heating device is a liquid-to-liquid heatexchanger. The first fluid stream may, in some cases, comprise a fluidstream that flows through a humidification region (e.g., ahumidification region liquid inlet stream) and/or a fluid stream thatflows through a dehumidification region (e.g., a dehumidification regionliquid outlet stream). The second fluid stream may, in some cases,comprise a heating fluid. The heating fluid may be any fluid capable ofabsorbing and transferring heat. In some embodiments, the heating fluidcomprises water (e.g., hot, pressurized water). In certain embodiments,heat may be transferred from the second fluid stream (e.g., the heatingfluid) to the first stream (e.g., the humidification region liquid inletstream, the dehumidification liquid outlet stream) in the heatexchanger. In some cases, more than two fluid streams may flow throughthe heat exchanger.

In some embodiments, the heating device is a heat collection device. Theheat collection device may be configured to store and/or utilize thermalenergy (e.g., in the form of combustion of natural gas, solar energy,waste heat from a power plant, or waste heat from combusted exhaust). Incertain cases, the heating device is configured to convert electricalenergy to thermal energy. For example, the heating device may be anelectric heater.

The heating device may, in some cases, increase the temperature of oneor more fluid streams (e.g., humidification region liquid inlet stream,dehumidification region liquid outlet stream) flowing through theheating device. For example, the difference between the temperature of afluid entering the heating device and the fluid exiting the heatingdevice may be at least about 5° C., at least about 10° C., at leastabout 15° C., at least about 20° C., at least about 30° C., at leastabout 40° C., at least about 50° C., at least about 60° C., at leastabout 70° C., at least about 80° C., or, in some cases, at least about90° C. In some embodiments, the difference between the temperature of afluid entering the heating device and the fluid exiting the heatingdevice may be in the range of about 5° C. to about 30° C., about 5° C.to about 60° C., about 5° C. to about 90° C., about 10° C. to about 30°C., about 10° C. to about 60° C., about 10° C. to about 90° C., about20° C. to about 60° C., about 20° C. to about 90° C., about 30° C. toabout 60° C., about 30° C. to about 90° C., or about 60° C. to about 90°C. In some cases, the temperature of a fluid stream (e.g.,humidification region liquid inlet stream, dehumidification regionliquid outlet stream) being heated in the heating device remains belowthe boiling point of the fluid stream.

In some embodiments, a desalination system may comprise two or moreheating devices. For example, in some embodiments, a first heatingdevice further heats a humidification region liquid inlet stream afterthe stream has flowed through a heat exchanger. In some embodiments, asecond heating device heats a dehumidification region liquid outletstream prior to the stream flowing through the heat exchanger. In someembodiments, the second heating device heats the humidification regionliquid inlet stream and the first heating device heats thedehumidification region liquid outlet stream. In some embodiments, asingle heating device may function as the first heating device andsecond heating device and heat both the humidification region liquidinput stream and the dehumidification region liquid outlet stream.Further, there may be any number of heating devices present in thedesalination system.

In some embodiments, an optional external cooling device may be arrangedin fluid communication with the combined HDH apparatus (e.g., combinedbubble column apparatus) and/or the external heat exchanger. In certaincases, the cooling device may be arranged such that, in operation, aheat exchanger outlet stream (e.g., a cooled dehumidification regionliquid outlet stream) is further cooled in the cooling device prior toreturning to the combined HDH apparatus (e.g., the dehumidificationregion of the combined HDH apparatus).

A cooling device generally refers to any device that is capable ofremoving heat from a fluid stream (e.g., a liquid stream, a gas stream).In some embodiments, the cooling device is a heat exchanger. The heatexchanger may be configured such that a first fluid stream and a secondfluid stream flow through the heat exchanger. In some cases, the firstfluid stream and the second fluid stream may flow in substantially thesame direction (e.g., parallel flow), substantially opposite directions(e.g., counter-flow), or substantially perpendicular directions (e.g.,cross flow). In some cases, heat is transferred from a first fluidstream to a second fluid stream. In certain embodiments, the coolingdevice is a liquid-to-gas heat exchanger. The first fluid stream may, incertain cases, comprise a fluid stream that is part of a loop ofcondenser liquid flowing between a condenser and a heat exchanger (e.g.,a dehumidification region liquid outlet stream). The second fluid streammay, in some cases, comprise a coolant. The coolant may be any fluidcapable of absorbing or transferring heat. In some embodiments, thecoolant comprises a gas. The gas may, in some cases, comprise air (e.g.,ambient air). Heat exchangers that comprise air as a coolant maygenerally be referred to as air-cooled heat exchangers. In some cases,more than two fluid streams flow through the cooling device. It shouldalso be noted that the cooling device may, in some embodiments, be a drycooler, a chiller, a radiator, or any other device capable of removingheat from a fluid stream.

The cooling device may, in some cases, decrease the temperature of afluid stream (e.g., a heat exchanger outlet stream, a dehumidificationregion liquid outlet stream). In some embodiments, the cooling devicedecreases the temperature of the fluid stream by at least about 5° C.,at least about 10° C., at least about 15° C., at least about 20° C., atleast about 30° C., at least about 40° C., at least about 50° C., atleast about 60° C., at least about 70° C., at least about 80° C., or, insome cases, at least about 90° C. In some embodiments, the coolingdevice decreases the temperature of the fluid stream by an amount in therange of about 5° C. to about 30° C., about 5° C. to about 60° C., about5° C. to about 90° C., about 10° C. to about 30° C., about 10° C. toabout 60° C., about 10° C. to about 90° C., about 20° C. to about 30°C., about 20° C. to about 60° C., about 20° C. to about 90° C., about30° C. to about 60° C., about 30° C. to about 90° C., or about 60° C. toabout 90° C.

FIG. 7B shows an exemplary embodiment of a system 700 comprising acombined HDH (e.g. bubble column) apparatus 702, an external heatexchanger 708, an external heating device 714, and an external coolingdevice 716. Humidification region 704, heat exchanger 708, and heatingdevice 714 are arranged to be in fluid communication with each otherthrough liquid conduit 712. Dehumidification region 706, heat exchanger708, and cooling device 716 are arranged to be in fluid communicationwith each other through liquid conduit 710.

In operation, in an exemplary embodiment, a humidification region liquidoutlet stream may exit humidification region 704 at a temperature T₁ andenter heat exchanger 708, and a dehumidification region liquid outletstream may exit dehumidification region 706 at a temperature T₂ and alsoenter heat exchanger 708. In some embodiments, the humidification regionliquid outlet stream and the dehumidification region liquid outletstream may flow through heat exchanger 708 in substantially oppositedirections (e.g., heat exchanger 708 is a counter-flow heat exchanger).As the humidification region liquid outlet stream and dehumidificationregion liquid outlet stream flow through heat exchanger 708, heat may betransferred from the dehumidification region liquid outlet stream to thehumidification region liquid outlet stream, such that the temperature ofthe humidification region liquid outlet stream is increased to atemperature T₃ greater than temperature T₁, and the temperature of thedehumidification region liquid outlet stream is decreased to atemperature T₄ lower than temperature T₂. The heated humidificationregion liquid outlet stream may then exit heat exchanger 708 and flowthrough heating device 714 to be further heated, with the temperature ofthe stream increasing from temperature T₃ to a temperature T₅, which isgreater than temperature T₃. The further heated humidification regionliquid outlet stream may then be returned to humidification region 704.Optionally, a first portion of the further heated humidification regionliquid outlet stream may be returned to humidification region 704, and asecond portion may be discharged from the system and/or routed toanother portion of the system. The cooled dehumidification region liquidoutlet stream may exit heat exchanger 708 and flow through coolingdevice 716 to be further cooled, with the temperature of the streamdecreasing from temperature T₄ to a temperature T₆, which is lower thantemperature T₄. The further cooled dehumidification region liquid outletstream may then be returned to dehumidification region 706.

In some embodiments, the desalination system may be fluidly connected toone or more additional devices. For example, the desalination system maybe fluidly connected to an optional pre-treatment system and/or anoptional precipitation apparatus. In some cases, a pre-treatment systemmay be configured to remove one or more components from a liquid feedstream entering the desalination system. In some cases, a precipitationapparatus may be configured to precipitate one or more solid salts froma liquid output stream of the desalination system comprising one or moredissolved salts.

FIG. 9 is a schematic diagram of exemplary system 900, according tocertain embodiments. In FIG. 9, system 900 comprises optionalpretreatment system 902, desalination system 916, and optionalprecipitation apparatus 918. As shown in FIG. 9, pretreatment system 902comprises optional separation apparatus 904 configured to remove atleast a portion of a suspended and/or emulsified immiscible phase from aliquid stream, optional ion-removal apparatus 906 configured to removeat least a portion of at least one scale-forming ion from a liquidstream, optional suspended solids removal apparatus 908 configured toremove at least a portion of suspended solids from a liquid stream,optional pH adjustment apparatus 910 configured to adjust (i.e. increaseor decrease) or maintain/stabilize (e.g. via buffering) the pH of aliquid stream, optional volatile organic material (VOM) removalapparatus 912 configured to remove at least a portion of VOM from aliquid stream, and/or optional filtration apparatus 914 configured toproduce a substantially solid material. Each component of system 900 maybe fluidly connected to one or more other components of system 900,either directly or indirectly. It should be noted that each of thecomponents of system 900 shown in FIG. 9 is optional, and a system maycomprise any combination of the components shown in FIG. 9. In someembodiments, desalination system 900 further comprises one or more feedtanks and/or one or more storage tanks (e.g., a tank to storesubstantially pure water) (not shown in FIG. 9).

In operation, liquid feed stream 920 comprising a suspended and/oremulsified immiscible phase, a scale-forming ion, suspended solids,and/or a volatile organic material is flowed to separation apparatus904. Separation apparatus 904 removes at least a portion of thesuspended and/or emulsified immiscible phase to produceimmiscible-phase-diminished stream 922, which contains less of theimmiscible phase than stream 920. In certain embodiments, separationapparatus 904 also produces immiscible-phase-enriched stream 924, whichcontains more of the immiscible phase than stream 920.Immiscible-phase-diminished stream 922 is then made to flow toion-removal apparatus 906. Ion-removal apparatus 906 removes at least aportion of at least one scale-forming ion from stream 922 to produceion-diminished stream 926, which contains less of at least onescale-forming ion than immiscible-phase-diminished stream 922. Incertain embodiments, ion-removal apparatus 906 also producesion-enriched stream 928, which contains more of at least onescale-forming ion than immiscible-phase-diminished stream 922.Ion-diminished stream 926 is then made to flow to suspended solidsremoval apparatus 908. Suspended solids removal apparatus 908 removes atleast a portion of suspended solids from ion-diminished stream 926 toproduce suspended-solids-diminished stream 930, which contains lesssuspended solids than ion-diminished stream 926. Optionally, suspendedsolids removal apparatus 908 may also produce suspended-solids-enrichedstream 932, which may be flowed to filtration apparatus 914 to formsolid stream 934 and filtered liquid stream 936.Suspended-solids-diminished stream 930 is then made to flow to pHadjustment apparatus 910. pH adjustment apparatus 910 may, in certaincases, increase or decrease the pH of stream 930 to produce stream 938.In some cases, chemicals 940 (e.g., one or more acids) may be added inpH adjustment apparatus 910 to adjust (e.g., increase or decrease) ormaintain/stabilize (e.g., via buffering) the pH of stream 930.pH-adjusted stream 938 is then made to flow to VOM removal apparatus912. VOM removal apparatus 912 may remove at least a portion of VOM frompH-adjusted stream 938 to produce VOM-diminished stream 942. VOM removalapparatus 912 may also produce VOM-enriched stream 944. VOM-diminishedstream 942 is then made to flow to desalination system 916, which may beconfigured to remove at least a portion of at least one dissolved saltfrom VOM-diminished stream 942. In some cases, desalination system 916is configured to produce a substantially pure water stream 946 and aconcentrated brine stream 948. In certain embodiments, at least aportion of substantially pure water stream 946 is discharged from system900 and/or is recycled and returned to desalination system 916. Incertain cases, at least a portion of concentrated brine stream 948 ismade to flow to precipitation apparatus 918. Precipitation apparatus 918may be configured such that at least a portion of the dissolved saltwithin concentrated brine stream 948 is precipitated withinprecipitation apparatus 918 to produce solid stream 950 andwater-containing stream 952, which contains less dissolved salt thanconcentrated brine stream 948.

In some cases, the precipitation apparatus comprises a vessel, such as asettling tank. The vessel may include an inlet through which at least aportion of a concentrated saline stream (e.g., a humidification regionliquid outlet stream) produced by the desalination system is transportedinto the precipitation vessel. The precipitation vessel may also includeat least one outlet. For example, the precipitation vessel may includean outlet through which a water-containing stream (containing adissolved salt in an amount that is less than that contained in theinlet stream) is transported. In some embodiments, the precipitationvessel includes an outlet through which solid, precipitated salt istransported.

In some embodiments, the settling tank comprises a low shear mixer. Thelow shear mixer can be configured to keep the crystals that are formedmixed (e.g., homogeneously mixed) in the concentrated saline stream.According to certain embodiments, the vessel is sized such that there issufficient residence time for crystals to form and grow. In certainembodiments, the precipitation apparatus comprises a vessel whichprovides at least 20 minutes of residence time for the concentratedsaline stream. As one non-limiting example, the vessel comprises,according to certain embodiments, a 6000 gallon vessel, which can beused to provide 24 minutes of residence in a 500 U.S. barrel per dayfresh water production system.

Those of ordinary skill in the art are capable of determining theresidence time of a volume of fluid in a vessel. For a batch (i.e.,non-flow) system, the residence time corresponds to the amount of timethe fluid spends in the vessel. For a flow-based system, the residencetime is determined by dividing the volume of the vessel by thevolumetric flow rate of the fluid through the vessel.

In some embodiments, the precipitation apparatus comprises at least onevessel comprising a volume within which the concentrated saline streamis substantially quiescent. In some embodiments, the flow velocity ofthe fluid within the substantially quiescent volume is less than theflow velocity at which precipitation (e.g., crystallization) isinhibited. For example, the fluid within the substantially quiescentvolume may have, in certain embodiments, a flow velocity of zero. Insome embodiments, the fluid within the substantially quiescent volumemay have a flow velocity that is sufficiently high to suspend the formedsolids (e.g., crystals), but not sufficiently high to prevent solidformation (e.g., crystal nucleation). The substantially quiescent volumewithin the vessel may occupy, in some embodiments, at least about 1%, atleast about 5%, at least about 10%, or at least about 25% of the volumeof the vessel. As one particular example, the precipitation apparatuscan comprise a vessel including a stagnation zone. The stagnation zonemay be positioned, for example, at the bottom of the precipitationvessel. In certain embodiments, the precipitation apparatus can includea second vessel in which the solids precipitated in the first vessel areallowed to settle. For example, an aqueous stream containing theprecipitated solids can be transported to a settling tank, where thesolids can be allowed to settle. The remaining contents of the aqueousstream can be transported out of the settling tank. While the use of twovessels within the precipitation apparatus has been described, it shouldbe understood that, in other embodiments, a single vessel, or more thantwo vessels may be employed. In certain embodiments, the desalinationsystem can be operated such that precipitation of the salt occurssubstantially only within the stagnation zone of the precipitationvessel.

In some embodiments, the precipitated salt from the precipitationapparatus is fed to a solids-handling apparatus. The solids-handlingapparatus may be configured, in certain embodiments, to remove at leasta portion of the water retained by the precipitated salt. In some suchembodiments, the solids-handling apparatus is configured to produce acake comprising at least a portion of the precipitated salt from theprecipitation apparatus. As one example, the solids-handling apparatuscan comprise a filter (e.g., a vacuum drum filter or a filter press)configured to at least partially separate the precipitated salt from theremainder of a suspension containing the precipitated salt. In some suchembodiments, at least a portion of the liquid within the salt suspensioncan be transported through the filter, leaving behind solid precipitatedsalt. As one non-limiting example, a Larox FP 2016-8000 64/64 M40 PP/PPFilter (Outotec, Inc.) may be used as the filter. The filter maycomprise, in certain embodiments, a conveyor filter belt which filtersthe salt from a suspension containing the salt.

It should be noted that while the combined HDH apparatuses describedherein have generally been discussed in the context of desalinationsystems, the apparatuses may be used in other types of systems (e.g.,other water treatment/purification systems). For example, the combinedHDH apparatuses may be used in separation processes to separate one ormore components of an input liquid stream (e.g., a liquid mixture). In aparticular, non-limiting embodiment, the combined HDH apparatuses may beused in distillation systems to distill certain liquids from liquidmixtures (e.g., ionic solutions). Examples of liquids that may bedistilled from liquid mixtures using the combined HDH apparatusesdescribed herein include, but are not limited to, ammonia, benzene,toluene, phenol, xylene, naphthalene, xylene, gasoline, methanol,ethanol, propanol, butanol, isopropyl alcohol, propylene glycol,hexane-n, heptane-n, octane-n, cyclohexane, acetic acid, formic acid,nitric acid, carbon tetrachloride, methyl acetate, and/or acetone.

Various of the components described herein can be “directly fluidlyconnected” to other components. As used herein, a direct fluidconnection exists between a first component and a second component (andthe two components are said to be “directly fluidly connected” to eachother) when they are fluidly connected to each other and the compositionof the fluid does not substantially change (i.e., no fluid componentchanges in relative abundance by more than 5% and no phase changeoccurs) as it is transported from the first component to the secondcomponent. As an illustrative example, a stream that connects first andsecond system components, and in which the pressure and temperature ofthe fluid is adjusted but the composition of the fluid is not altered,would be said to directly fluidly connect the first and secondcomponents. If, on the other hand, a separation step is performed and/ora chemical reaction is performed that substantially alters thecomposition of the stream contents during passage from the firstcomponent to the second component, the stream would not be said todirectly fluidly connect the first and second components.

Other examples of HDH systems are described in U.S. Pat. No. 8,292,272,by Elsharqawy et al., issued Oct. 23, 2012, entitled “Water SeparationUnder Reduced Pressure”; U.S. Pat. No. 8,465,006, by Elsharqawy et al.,issued Jun. 18, 2013, entitled “Separation of a Vaporizable ComponentUnder Reduced Pressure”; U.S. Pat. No. 8,252,092, by Govindan et al.,issued Aug. 28, 2012, entitled “Water Separation Under Varied Pressure”;U.S. Pat. No. 8,496,234, by Govindan et al., issued Jul. 30, 2013,entitled “Thermodynamic Balancing of Combined Heat and Mass ExchangeDevices”; U.S. Pat. No. 8,523,985, by Govindan et al., issued Sep. 3,2013, entitled “Bubble-Column Vapor Mixture Condenser”; U.S. Pat. No.8,778,065, by Govindan et al., issued Jul. 15, 2014, entitled“Humidification-Dehumidification System Including a Bubble-Column VaporMixture Condenser”; U.S. Patent Publication No. 2013/0074694, byGovindan et al., filed Sep. 23, 2011, entitled “Bubble-Column VaporMixture Condenser”; U.S. Patent Publication No. 2015/0129410, byGovindan et al., filed Sep. 12, 2014, entitled “Systems Including aCondensing Apparatus Such as a Bubble Column Condenser”; andInternational Patent Publication No. WO 2014/200829, by Govindan et al.,filed Jun. 6, 2014, as International Patent Application No.PCT/US2014/041226, and entitled “Multi-Stage Bubble Column Humidifier,”the contents of all of which are incorporated herein by reference intheir entireties for all purposes.

Example

As shown in FIG. 8, this example describes desalination system 800,which comprises combined bubble column apparatus 802, precipitationapparatus 834, first heat exchanger 836, second heat exchanger 838, andcooling device 840. Desalination system 800 is configured to produce 850barrels of substantially pure water per day.

Combined bubble column apparatus 802 comprises humidification region 804and dehumidification region 806 positioned vertically abovehumidification region 804. As shown in FIG. 8, apparatus 802 furthercomprises gas distribution chamber 808 positioned vertically belowhumidification region 804. In FIG. 8, gas distribution chamber 808 is influid communication with apparatus air inlet 810 and humidificationregion brine outlet 812. In some cases, gas distribution chamber 808comprises a liquid sump volume and a gas distribution region positionedabove the liquid sump volume. Humidification region 804 comprises aplurality of stages 814A-F that are vertically arranged above gasdistribution chamber 808. Each of stages 814A-F is coupled to a bubblegenerator and comprises a liquid layer and a vapor distribution regionpositioned above the liquid layer. As shown in FIG. 8, third stage 814Cis fluidly connected to intermediate air outlet 816, and sixth stage814F (e.g., the topmost stage of humidification region 804) is fluidlyconnected to humidification region brine inlet 818. Dehumidificationregion 806 comprises a plurality of vertically-arranged stages 820A-F,each stage coupled to a bubble generator and comprising a liquid layerand a vapor distribution region positioned above the liquid layer. Aliquid collection region positioned below first stage 820A is fluidlyconnected to dehumidification region water outlet 822, and sixth stage820F (e.g., the topmost stage of dehumidification region 806) is fluidlyconnected to dehumidification region water inlet 824 and apparatus airoutlet 826. In addition, third stage 820C is fluidly connected tointermediate air inlet 828, which is fluidly connected to intermediateair outlet 816 through a gas conduit. Droplet eliminator 830 and liquidcollector 832 are positioned between humidification region 804 anddehumidification region 806.

In addition to combined bubble column apparatus 802, desalination system800 comprises precipitation apparatus 834, first heat exchanger 836,second heat exchanger 838, cooling device 840, solid conduit 842, andliquid conduits 844, 846, 848, 850, 852, and 854. Precipitationapparatus 834 is directly fluidly connected to humidification regionbrine outlet 812 and first heat exchanger 836. First heat exchanger 836,in addition to being directly fluidly connected to precipitationapparatus 834, is directly fluidly connected to dehumidification regionwater outlet 822, second heat exchanger 838, and cooling device 840.Additionally, second heat exchanger 838 is directly fluidly connected tohumidification region brine inlet 818, and cooling device 840 isdirectly fluidly connected to dehumidification region water inlet 824.

In operation, ambient air enters humidification region 804 of combinedbubble column apparatus 802 through apparatus air inlet 810. The ambientair enters humidification region 804 at a flow rate of 8330 actual cubicfeet per minute (acfm) and a temperature of 60° F. The stream of ambientair flows upwards through each of stages 814A, 814B, 814C, 814D, 814E,and 814F of humidification region 804. Meanwhile, a stream comprisingsalt-containing water enters humidification region 804 throughhumidification region brine inlet 818 at a flow rate of 632 gallons perminute (gpm) and a temperature of 200° F. The salt-containing waterstream flows in a direction substantially opposite to the direction ofthe flow of the air stream (e.g., downwards through each of stages 814F,814E, 814D, 814C, 814B, and 814A of humidification region 804). Each ofstages 814A-F is at least partially occupied by a liquid layercomprising the salt-containing water. Accordingly, as the air streamflows upwards through the stages of humidification region 804, each ofwhich is coupled to a bubble generator, air bubbles form and travelthrough the liquid layers comprising the salt-containing water, whichhas a higher temperature than the air bubbles. As the air bubbles comeinto direct contact with the salt-containing water of the liquid layers,heat and mass (e.g., water vapor) are transferred from thesalt-containing water to the air bubbles, and the air bubbles becomeincreasingly heated and humidified. Within the vapor distribution regionof each stage, heated and at least partially humidified air bubblesrecombine to form an air stream that is substantially evenly distributedthroughout the vapor distribution region. The substantially evenlydistributed air stream may then pass through a bubble generator coupledto the next stage and flow through the liquid layer of that next stage,becoming further heated and humidified. When the air stream reachesthird stage 814C, at least a portion of the heated and at leastpartially humidified air stream exits humidification region 804 throughintermediate air outlet 816 at a flow rate of 8000 acfm and atemperature of 160° F. The remaining portion of the air stream continuesto flow upwards through the vertically-arranged stages 814D-F ofhumidification region 804.

After flowing through stages 814A-F of humidification region 804, theheated, at least partially humidified air stream flows through dropleteliminator 830 and liquid collector 832 and enters dehumidificationregion 806. The heated, at least partially humidified air stream flowsupwards through each of stages 820A, 820B, 820C, 820D, 820E, and 820F ofdehumidification region 806. Meanwhile, a stream of substantially purewater enters dehumidification region 806 through dehumidification regionwater inlet 824 at a flow rate of 550 gpm and a temperature of 125° F.The substantially pure water stream flows in a direction substantiallyopposite to the direction of the flow of the air stream (e.g., downwardsthrough each of stages 820F, 820E, 820D, 820C, 820B, and 820A ofdehumidification region 806). Each of stages 820A-F is at leastpartially occupied by a liquid layer comprising the substantially purewater. Accordingly, as the heated, at least partially humidified airstream flows upwards through the stages of dehumidification region 806,each of which is coupled to a bubble generator, heated, at leastpartially humidified air bubbles form and travel through the liquidlayers comprising the substantially pure water, which has a lowertemperature than the heated, at least partially humidified air bubbles.As the air bubbles come into direct contact with the substantially purewater, heat and mass (e.g., water vapor) are transferred from the airbubbles to the substantially pure water of the liquid layers, and theair bubbles become increasingly cooled and dehumidified. Within thevapor distribution region of each stage, cooled, at least partiallydehumidified air bubbles recombine to form an air stream that issubstantially evenly distributed throughout the vapor distributionregion. In third stage 820C, heated, at least partially humidified airextracted from intermediate air outlet 816 enters dehumidificationregion 806 and joins the air stream flowing through dehumidificationregion 806. After flowing through each of stages 820A-F ofdehumidification region 806, the cooled, at least partially dehumidifiedair stream exits combined bubble column apparatus 802 through apparatusgas outlet 826.

As noted above, two liquid streams—a substantially pure water stream anda salt-containing water stream—flow through combined bubble columnapparatus 802 counter-flow to the air stream. The salt-containing waterstream, which comprises water and at least one dissolved salt, entershumidification region 804 of combined bubble column apparatus 802through humidification region brine inlet 818 and flows downwardsthrough each of stages 814A-F of humidification region 804 to gasdistribution chamber 808. As the salt-containing water stream flowsdownwards through each stage of humidification region 804, thesalt-containing water stream encounters air bubbles having a temperaturelower than the temperature of the salt-containing water stream, and heatand mass (e.g., water vapor) are transferred from the salt-containingwater stream to the air bubbles, thereby resulting in a cooled,concentrated salt-containing water stream. As the salt-containing waterstream flows through each stage of humidification region 804, theconcentration of at least one dissolved salt in the salt-containingwater stream increases (e.g., due to evaporation of water). The cooled,concentrated salt-containing water stream then exits apparatus 802through humidification region brine outlet 812 at a flow rate of 593 gpmand a temperature of 136° F. The cooled, concentrated salt-containingwater stream is then made to flow to precipitation apparatus 834, and atleast a portion of at least one dissolved salt in the salt-containingwater stream may precipitate within the precipitation apparatus. Theprecipitated salt may be discharged from system 800 through solidconduit 842. The remaining liquid portion of the salt-containing waterstream exits precipitation apparatus 834 as a precipitation apparatusliquid outlet stream. In some cases, at least a portion of theprecipitation apparatus liquid outlet stream is discharged fromdesalination system 800 through conduit 844 at a flow rate of 593 gpm.Another portion of the precipitation apparatus liquid outlet stream mayremain in desalination system 800. In some cases, additionalsalt-containing water may enter desalination system 800 through conduit846 at a flow rate of 25 gpm and a temperature of 60° F. The additionalsalt-containing water may combine with the portion of the precipitationapparatus liquid outlet stream remaining in desalination system 800. Thecombined salt-containing water stream then flows through conduit 848 tofirst heat exchanger 836, entering first heat exchanger 836 at a flowrate of 632 gpm and a temperature of 130° F. As noted above, first heatexchanger 836 is also directly fluidly connected to dehumidificationregion water outlet 822, and a substantially pure water stream entersfirst heat exchanger 836 at a flow rate of 575 gpm and a temperature of170° F. As the salt-containing water stream and substantially pure waterstream flow through first heat exchanger 836, heat is transferred fromthe substantially pure water stream to the salt-containing water stream,producing a heated salt-containing water stream that exits first heatexchanger 836 at a temperature of 160° F. and a cooled substantiallypure water stream that exits heat exchanger 836 at a temperature of 140°F. The heated salt-containing water stream is then made to flow tosecond heat exchanger 838 to be further heated. As the heatedsalt-containing water stream enters second heat exchanger 838 at a flowrate of 632 gpm and a temperature of 160° F. and flows through secondheat exchanger 838, a heating fluid also flows through second heatexchanger 838 via conduit 850. Heat is transferred from the heatingfluid to the heated salt-containing water stream to produce a furtherheated salt-containing water stream having a temperature of 200° F. Thefurther heated salt-containing water stream then returns tohumidification region 804 of apparatus 802 through humidification regionbrine inlet 818 at a flow rate of 632 gpm and a temperature of 200° F.

In addition to the salt-containing water stream, a substantially purewater stream flows through combined bubble column apparatus 802. Thesubstantially pure water stream enters dehumidification region 806 ofapparatus 802 through dehumidification region water inlet 824 at a flowrate of 550 gpm and a temperature of 125° F. As the substantially purewater stream flows downwards through each of stages 820A-F ofdehumidification region 806, the substantially pure water streamencounters bubbles of heated, at least partially humidified air, andheat and mass (e.g., water vapor) are transferred from the heated, atleast partially humidified air bubbles to the substantially pure waterstream, thereby resulting in a heated substantially pure water stream.As the substantially pure water stream flows downwards through each ofthe stages of dehumidification region 806, the temperature of thesubstantially pure water stream increases. The heated substantially purewater stream then exits apparatus 802 through dehumidification regionwater outlet 822 at a flow rate of 575 gpm and a temperature of 170° F.After exiting apparatus 802, the heated substantially pure water streamis made to flow through first heat exchanger 836, where heat istransferred from the heated substantially pure water stream to theprecipitation apparatus liquid outlet stream (e.g., a portion of thecooled, concentrated salt-containing water stream that exited apparatus802 through humidification region brine outlet 812) to produce a cooledsubstantially pure water stream. The cooled substantially pure waterstream exits first heat exchanger 836 at a temperature of 140° F. Insome cases, at least a portion of the cooled substantially pure waterstream exits desalination system 802 through conduit 852 at a flow rateof 25 gpm and a temperature of 140° F. In some embodiments, at least aportion of the cooled substantially pure water stream remains indesalination system 802 and is made to flow through conduit 854 tocooling device 840. The cooled substantially pure water stream enterscooling device 840, which may be an air-cooled heat exchanger, at a flowrate of 550 gpm and a temperature of 135° F. As the cooled substantiallypure water stream flows through cooling device 840, the stream isfurther cooled to a temperature of 125° F. The further cooledsubstantially pure water stream then returns to combined bubble columnapparatus 802, entering dehumidification region 806 of apparatus 802through dehumidification region water inlet 824 at a flow rate of 550gpm and a temperature of 125° F.

While several embodiments of the present invention have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the present invention.More generally, those skilled in the art will readily appreciate thatall parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the teachings of thepresent invention is/are used. Those skilled in the art will recognize,or be able to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described and claimed. Thepresent invention is directed to each individual feature, system,article, material, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,and/or methods, if such features, systems, articles, materials, and/ormethods are not mutually inconsistent, is included within the scope ofthe present invention.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Other elements may optionallybe present other than the elements specifically identified by the“and/or” clause, whether related or unrelated to those elementsspecifically identified unless clearly indicated to the contrary. Thus,as a non-limiting example, a reference to “A and/or B,” when used inconjunction with open-ended language such as “comprising” can refer, inone embodiment, to A without B (optionally including elements other thanB); in another embodiment, to B without A (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc. In theclaims, as well as in the specification above, all transitional phrasessuch as “comprising,” “including,” “carrying,” “having,” “containing,”“involving,” “holding,” and the like are to be understood to beopen-ended, i.e., to mean including but not limited to. Only thetransitional phrases “consisting of” and “consisting essentially of”shall be closed or semi-closed transitional phrases, respectively, asset forth in the United States Patent Office Manual of Patent ExaminingProcedures, Section 2111.03.

In cases where the present specification and a document incorporated byreference, attached as an appendix, and/or referred to herein includeconflicting disclosure, and/or inconsistent use of terminology, and/orthe incorporated/appended/referenced documents use or define termsdifferently than they are used or defined in the present specification,the present specification shall control.

What is claimed is:
 1. A desalination system, comprising: a vessel,comprising: a humidification region comprising a humidification regionliquid inlet fluidly connected to a source of salt-containing water, ahumidification region gas inlet fluidly connected to a source of a gas,and a humidification region gas outlet, wherein the humidificationregion is configured to produce a vapor-containing humidification regiongas outlet stream enriched in water vapor relative to the gas receivedfrom the gas inlet; and a dehumidification region comprising adehumidification region gas inlet fluidly connected to thehumidification region gas outlet, a dehumidification region gas outlet,and a dehumidification region water outlet, wherein the dehumidificationregion is configured to remove at least a portion of the water vaporfrom the vapor-containing humidification region gas outlet stream toproduce a dehumidification region water outlet stream and adehumidification gas outlet stream lean in water vapor relative to thehumidification region gas outlet stream; and a heat exchanger separatefrom the vessel, wherein the heat exchanger is fluidly connected to thedehumidification region water outlet and the humidification regionliquid inlet, wherein the heat exchanger is configured to transfer heatfrom the dehumidification region water outlet stream to thehumidification region liquid inlet stream to produce a cooleddehumidification region water outlet stream and a heated humidificationregion liquid inlet stream.
 2. (canceled)
 3. A desalination system,comprising: a vessel, comprising: a humidification region comprising ahumidification region liquid inlet fluidly connected to a source ofsalt-containing water, a humidification region gas inlet fluidlyconnected to a source of a gas, and a humidification region gas outlet,wherein the humidification region is configured to produce avapor-containing humidification region gas outlet stream enriched inwater vapor relative to the gas received from the gas inlet; and adehumidification region comprising a dehumidification region gas inletfluidly connected to the humidification region gas outlet, adehumidification region gas outlet, and a dehumidification region wateroutlet, wherein the dehumidification region is configured to remove atleast a portion of the water vapor from the vapor-containinghumidification region gas outlet stream to produce a dehumidificationregion water outlet stream and a dehumidification gas outlet stream leanin water vapor relative to the humidification region gas outlet stream,wherein a portion of a gas stream is extracted from at least oneintermediate location in the humidification region and fed to at leastone intermediate location in the dehumidification region.
 4. (canceled)5. The desalination system of claim 1, wherein the gas comprises anon-condensable gas.
 6. (canceled)
 7. The desalination system of claim1, wherein the salt-containing water comprises seawater, brackish water,flowback water, water produced from an oil or gas extraction process,and/or wastewater. 8-10. (canceled)
 11. The desalination system of claim1, wherein the humidification region and/or dehumidification regioncomprise at least one chamber fluidly connected to a bubble generator.12. (canceled)
 13. The desalination system of claim 1, wherein thehumidification region and/or dehumidification region comprise a firststage comprising a first stage gas inlet, a first stage gas outlet, anda first stage chamber comprising a liquid layer, wherein the first stagegas inlet is fluidly coupled to one or more bubble generators.
 14. Thedesalination system of claim 13, wherein the humidification regionand/or dehumidification region further comprise a second stagecomprising a second stage gas inlet, a second stage gas outlet, and asecond stage chamber comprising a liquid layer, wherein the second stagegas inlet is in fluid communication with the first stage gas outlet andis fluidly coupled to one or more bubble generators. 15-18. (canceled)19. The desalination system of claim 1, wherein the humidificationregion is configured to flow a salt-containing water stream in a firstdirection and the vapor-containing humidification region gas outletstream in a second, substantially opposite direction, and wherein thedehumidification region is configured to flow the dehumidificationregion water outlet stream in a first direction and the vapor-containinghumidification region gas outlet stream in a second, substantiallyopposite direction.
 20. (canceled)
 21. The desalination system of claim1, wherein the vessel comprises a first gas inlet in fluid communicationwith a source of a first gas and a second gas inlet in fluidcommunication with a source of a second gas. 22-23. (canceled)
 24. Thedesalination system of claim 1, wherein the humidification region and/orthe dehumidification region comprise at least one chamber comprising aliquid layer and a vapor distribution region positioned above the liquidlayer. 25-27. (canceled)
 28. The desalination system of claim 1, whereinthe dehumidification region is configured to receive at least a portionof the cooled dehumidification region water outlet stream. 29-30.(canceled)
 31. The desalination system of claim 1, wherein the heatexchanger is configured to receive the dehumidification region wateroutlet stream at a first heat exchanger inlet temperature and producethe cooled dehumidification region water outlet stream at a first heatexchanger outlet temperature, and the difference between the first heatexchanger inlet temperature and the first heat exchanger outlettemperature is in the range of about 10° C. to about 90° C.
 32. Thedesalination system of claim 1, wherein the heat exchanger is configuredto receive the humidification region liquid inlet stream at a secondheat exchanger inlet temperature and produce the heated humidificationregion liquid inlet stream at a second heat exchanger outlettemperature, and the difference between the second heat exchanger outlettemperature and the second heat exchanger inlet temperature is in therange of about 10° C. to about 90° C.
 33. The desalination system ofclaim 1, further comprising a cooling device separate from the vessel,wherein the cooling device is fluidly connected to the dehumidificationregion and/or the heat exchanger.
 34. (canceled)
 35. The desalinationsystem of claim 33, wherein the cooling device is configured to receivea cooling device input stream at a cooling device inlet temperature andto produce a cooling device output stream at a cooling device outlettemperature, wherein the difference between the cooling device inlettemperature and the cooling device outlet temperature is in the range ofabout 10° C. to about 90° C. 36-38. (canceled)
 39. The desalinationsystem of claim 33, wherein the cooling device is an air-cooled heatexchanger.
 40. The desalination system of claim 1, further comprising afirst heating device separate from the vessel, wherein the first heatingdevice is fluidly connected to the humidification region and/or the heatexchanger.
 41. (canceled)
 42. The desalination system of claim 40,wherein the first heating device is configured to receive a firstheating device input stream at a first heating device inlet temperatureand to produce a first heating device output stream at a first heatingdevice outlet temperature, wherein the difference between the firstheating device outlet temperature and the first heating device inlettemperature is in the range of about 10° C. to about 90° C. 43-45.(canceled)
 46. The desalination system of claim 1, further comprising asecond heating device separate from the vessel, wherein the secondheating device is fluidly connected to the dehumidification regionand/or the heat exchanger.
 47. (canceled)
 48. The desalination system ofclaim 46, wherein the second heating device is configured to receive asecond heating device input stream at a second heating device inlettemperature and to produce a second heating device output stream at asecond heating device outlet temperature, wherein the difference betweenthe second heating device outlet temperature and the second heatingdevice inlet temperature is in the range of about 10° C. to about 90° C.49-53. (canceled)